Antigen-binding molecule capable of binding two or more antigen molecules repeatedly

ABSTRACT

The present inventors discovered that antibodies having weaker antigen-binding activity at the early endosomal pH in comparison with that at the pH of plasma are capable of binding to multiple antigen molecules with a single antibody molecule, have long half-lives in plasma, and have improved durations of time in which they can bind to antigen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/595,139, filed on Aug. 27, 2012, which is a continuation of U.S.application Ser. No. 12/936,587, having a 371(c) date of Jan. 3, 2011,which is the National Stage of International Application Serial No.PCT/JP2009/057309, filed on Apr. 10, 2009, which claims priority toJapanese Application Nos. 2008-104147, filed on Apr. 11, 2008;2008-247713, filed on Sep. 26, 2008; and 2009-068744, filed on Mar. 19,2009, each of which is incorporated herein by reference.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

The content of the electronically submitted sequence listing (Name:6663_0068_Sequence_Listing.txt; Size: 119,858 bytes; and Date ofCreation: Apr. 13, 2018) filed with the application is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to methods for improving thepharmacokinetics of antigen-binding molecules and methods for increasingthe number of times of antigen-binding of antigen-binding molecules, aswell as antigen-binding molecules having improved pharmacokinetics,antigen-binding molecules having increased number of times ofantigen-binding, and methods for producing such molecules.

BACKGROUND ART

Antibodies are drawing attention as pharmaceuticals as they are highlystable in plasma and have few adverse effects. At present, a number ofIgG-type antibody pharmaceuticals are available on the market and manymore antibody pharmaceuticals are currently under development(Non-Patent Documents 1 and 2). Meanwhile, various technologiesapplicable to second-generation antibody pharmaceuticals have beendeveloped, including those that enhance effector function,antigen-binding ability, pharmacokinetics, and stability, and those thatreduce the risk of immunogenicity (Non-Patent Document 3). In general,the requisite dose of an antibody pharmaceutical is very high. This, inturn, has led to problems, such as high production cost, as well as thedifficulty in producing subcutaneous formulations. In theory, the doseof an antibody pharmaceutical may be reduced by improving antibodypharmacokinetics or improving the affinity between antibodies andantigens.

The literature has reported methods for improving antibodypharmacokinetics using artificial substitution of amino acids inconstant regions (Non-Patent Documents 4 and 5). Similarly, affinitymaturation has been reported as a technology for enhancingantigen-binding ability or antigen-neutralizing activity (Non-PatentDocument 6). This technology enables enhancement of antigen-bindingactivity by introduction of amino acid mutations into the CDR region ofa variable region or such. The enhancement of antigen-binding abilityenables improvement of in vitro biological activity or reduction ofdosage, and further enables improvement of in vivo efficacy (Non-PatentDocument 7).

The antigen-neutralizing capacity of a single antibody molecule dependson its affinity. By increasing the affinity, an antigen can beneutralized by smaller amount of an antibody. Various methods can beused to enhance the antibody affinity. Furthermore, if the affinitycould be made infinite by covalently binding the antibody to theantigen, a single antibody molecule could neutralize one antigenmolecule (a divalent antibody can neutralize two antigen molecules).However, the stoichiometric neutralization of one antibody against oneantigen (one divalent antibody against two antigens) is the limit ofpre-existing methods, and thus it is impossible to completely neutralizeantigen with the smaller amount of antibody than the amount of antigen.In other words, the affinity enhancing effect has a limit (Non-PatentDocument 9). To prolong the neutralization effect of a neutralizingantibody for a certain period, the antibody must be administered at adose higher than the amount of antigen produced in the body during thesame period. With the improvement of antibody pharmacokinetics oraffinity maturation technology alone described above, there is thus alimitation in the reduction of the required antibody dose.

Accordingly, in order to sustain antibody's antigen-neutralizing effectfor a target period with smaller amount of the antibody than the amountof antigen, a single antibody must neutralize multiple antigens. Methodsfor neutralizing multiple antigens with a single antibody includeantigen inactivation using catalytic antibodies, which are antibodiesconferred with a catalytic function. When the antigen is a protein, itcan be inactivated by hydrolyzing its peptide bonds. An antibody canrepeatedly neutralize antigens by catalyzing such hydrolysis (Non-PatentDocument 8). There are many previous reports published on catalyticantibodies and technologies for producing them. However, there have beenno reports of catalytic antibodies having sufficient catalytic activityas a pharmaceutical agent. Specifically, in an antibody in vivo studyfor a certain antigen, there has been no publication of catalyticantibodies which can produce a comparable or stronger effect even at lowdoses or produce a more prolonged effect even at a same dose as comparedto an ordinary non-catalytic neutralizing antibody.

As described above, there have been no reports of antibodies that canproduce a more superior in vivo effect than ordinary neutralizingantibodies through a single antibody neutralizing multiple antigenmolecules. Thus, from the viewpoint of dose reduction and prolongationof the durability, there is a need for new technologies that permit theproduction of novel antibody molecules having a stronger in vivo effectthan ordinary neutralizing antibodies by individually neutralizingmultiple antigen molecules.

Prior art documents related to the present invention are shown below:

PRIOR ART DOCUMENTS Non-Patent Documents

-   Non-Patent Document 1: Monoclonal antibody successes in the clinic.    Janice M Reichert, Clark J Rosensweig, Laura B Faden & Matthew C    Dewitz, Nature Biotechnology 23, 1073-1078 (2005)-   Non-Patent Document 2: Pavlou A K, Belsey M J. The therapeutic    antibodies market to 2008. Eur J Pharm Biopharm. 2005 April;    59(3):389-96-   Non-Patent Document 3: Kim S J, Park Y, Hong H J. Antibody    engineering for the development of therapeutic antibodies. Mol    Cells. 2005 Aug. 31; 20(1):17-29. Review-   Non-Patent Document 4: Hinton P R, Xiong J M, Johlfs M G, Tang M T,    Keller S, Tsurushita N. An engineered human IgG1 antibody with    longer serum half-life. J Immunol. 2006 Jan. 1; 176(1):346-56-   Non-Patent Document 5: Ghetie V, Popov S, Borvak J, Radu C, Matesoi    D, Medesan C, Ober R J, Ward E S. Increasing the serum persistence    of an IgG fragment by random mutagenesis. Nat Biotechnol. 1997 July;    15(7):637-40-   Non-Patent Document 6: Rajpal A, Beyaz N, Haber L, Cappuccilli G,    Yee H, Bhatt R R, Takeuchi T, Lerner R A, Crea R. A general method    for greatly improving the affinity of antibodies by using    combinatorial libraries. Proc Natl Acad Sci USA. 2005 Jun. 14;    102(24):8466-71. Epub 2005 June-   Non-Patent Document 7: Wu H, Pfarr D S, Johnson S, Brewah Y A, Woods    R M, Patel N K, White W I, Young J F, Kiener P A. Development of    Motavizumab, an Ultra-potent Antibody for the Prevention of    Respiratory Syncytial Virus Infection in the Upper and Lower    Respiratory Tract. J Mol Biol. 2007, 368, 652-665-   Non-Patent Document 8: Hanson C V, Nishiyama Y, Paul S. Catalytic    antibodies and their applications. Curr Opin Biotechnol. 2005    December; 16(6):631-6-   Non-Patent Document 9: Rathanaswami P, Roalstad S, Roskos L, Su Q J,    Lackie S, Babcook J. Demonstration of an in vivo generated    sub-picomolar affinity fully human monoclonal antibody to    interleukin-8. Biochem Biophys Res Commun. 2005 Sep. 9;    334(4):1004-13

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The above noted circumstances led to the discoveries of the presentinvention. Accordingly, an objective of the present invention is toprovide methods for binding antigen-binding molecules to the antigensmultiple times and methods for improving the pharmacokinetics ofantigen-binding molecules, as well as antigen-binding molecules that arecapable of binding to the antigens multiple times, antigen-bindingmolecules having improved pharmacokinetics, pharmaceutical compositionscontaining such antigen-binding molecules, and methods for producingsuch molecules and compositions.

Means for Solving the Problems

Dedicated studies on methods for binding polypeptides havingantigen-binding ability, such as antigen-binding molecules, to theantigens multiple times, and methods for improving the half-lives ofsuch molecules in plasma (blood) (improving their pharmacokinetics) wereconducted herein. As a result, it was discovered that if theantigen-binding activity of an antigen-binding molecule at the earlyendosomal pH is lower than its antigen-binding activiy at the pH ofplasma (blood), it would be able to bind to antigens multiple times andhave a longer half-life in plasma.

Accordingly, the present invention relates to methods for bindingantigen-binding molecules to antigens multiple times, methods forimproving the pharmacokinetics of antigen-binding molecules, and methodsfor producing antigen-binding molecules with improved pharmacokinetics;the present invention also relates to antigen-binding molecules that arecapable of binding to antigens multiple times and antigen-bindingmolecules with improved pharmacokinetics. More specifically, the presentinvention provides:

-   -   [1] an antigen-binding molecule having a KD(pH5.8)/KD(pH7.4)        value, defined as the ratio of KD for the antigen at pH 5.8 and        KD for the antigen at pH 7.4, of 2 or higher;    -   [2] the antigen-binding molecule of [1], wherein the        KD(pH5.8)/KD(pH7.4) value is 10 or higher;    -   [3] the antigen-binding molecule of [1], wherein the        KD(pH5.8)/KD(pH7.4) value is 40 or higher;    -   [4] the antigen-binding molecule of any one of [1] to [3],        wherein at least one amino acid of the antigen-binding molecule        has been substituted with histidine, or at least one histidine        has been inserted into the antigen-binding molecule;    -   [5] the antigen-binding molecule of any one of [1] to [4],        wherein the antigen-binding molecule has an antagonistic        activity;    -   [6] the antigen-binding molecule of any one of [1] to [5],        wherein the antigen-binding molecule binds to a membrane antigen        or a soluble antigen;    -   [7] the antigen-binding molecule of any one of [1] to [6],        wherein the antigen-binding molecule is an antibody;    -   [8] a pharmaceutical composition comprising the antigen-binding        molecule of any one of [1] to [7];    -   [9] a method for improving the pharmacokinetics of an        antigen-binding molecule by impairing the antigen-binding        activity of the antigen-binding molecule at pH 5.8 as compared        to that at pH 7.4;    -   [10] a method for increasing the number of times of        antigen-binding for an antigen-binding molecule by impairing the        antigen-binding activity of the antigen-binding molecule at pH        5.8 as compared to that at pH 7.4;    -   [11] a method for increasing the number of antigens that can be        bound by an antigen-binding molecule by impairing the        antigen-binding activity of the antigen-binding molecule at pH        5.8 as compared to that at pH 7.4;    -   [12] a method for dissociating within a cell an antigen from an        extracellularly-bound antigen-binding molecule by impairing the        antigen-binding activity of the antigen-binding molecule at pH        5.8 as compared to that at pH 7.4;    -   [13] a method for releasing an antigen-binding molecule, which        has been bound to an antigen and internalized into a cell, in an        antigen-free form to the outside of the cell by impairing the        antigen-binding activity of the antigen-binding molecule at pH        5.8 as compared to that at pH 7.4;    -   [14] a method for increasing the ability of an antigen-binding        molecule to eliminate an antigen in plasma by impairing the        antigen-binding activity of the antigen-binding molecule at pH        5.8 as compared to that at pH 7.4;    -   [15] the method of any one of [9] to [14], wherein the        KD(pH5.8)/KD(pH7.4) value, defined as the ratio of KD for the        antigen at pH 5.8 and KD for the antigen at pH 7.4, is 2 or        higher;    -   [16] the method of any one of [9] to [14], wherein the        KD(pH5.8)/KD(pH7.4) value is 10 or higher;    -   [17] the method of any one of [9] to [14], wherein the        KD(pH5.8)/KD(pH7.4) value is 40 or higher;    -   [18] a method for improving the pharmacokinetics of an        antigen-binding molecule by substituting at least one amino acid        of the antigen-binding molecule with histidine, or inserting at        least one histidine into the antigen-binding molecule;    -   [19] a method for increasing the number of times of        antigen-binding for an antigen-binding molecule by substituting        at least one amino acid of the antigen-binding molecule with        histidine, or inserting at least one histidine into the        antigen-binding molecule;    -   [20] a method for increasing the number of antigens that can be        bound by an antigen-binding molecule by substituting at least        one amino acid of the antigen-binding molecule with histidine,        or inserting at least one histidine into the antigen-binding        molecule;    -   [21] a method for dissociating within a cell an antigen from an        extracellularly-bound antigen-binding molecule by substituting        at least one amino acid of the antigen-binding molecule with        histidine, or inserting at least one histidine into the        antigen-binding molecule;    -   [22] a method for releasing an antigen-binding molecule, which        has been bound to an antigen and internalized into a cell, in an        antigen-free form to the outside of the cell, by substituting at        least one amino acid of the antigen-binding molecule with        histidine, or inserting at least one histidine into the        antigen-binding molecule;    -   [23] a method for increasing the ability of an antigen-binding        molecule to eliminate an antigen in plasma by substituting at        least one amino acid of the antigen-binding molecule with        histidine, or inserting at least one histidine into the        antigen-binding molecule;    -   [24] the method of any one of [18] to [23], wherein the        histidine substitution or insertion increases the        KD(pH5.8)/KD(pH7.4) value, defined as the ratio of the        antigen-binding activity at pH 5.8 and the antigen-binding        activity at pH 7.4, as compared to the KD(pH5.8)/KD(pH7.4) value        before the histidine substitution or insertion;    -   [25] the method of any one of [9] to [24], wherein the        antigen-binding molecule has an antagonistic activity;    -   [26] the method of any one of [9] to [25], wherein the        antigen-binding molecule binds to a membrane antigen or a        soluble antigen;    -   [27] the method of any one of [9] to [26], wherein the        antigen-binding molecule is an antibody;    -   [28] a method of screening for an antigen-binding molecule,        which comprises the steps of:        -   (a) determining the antigen-binding activity of an            antigen-binding molecule at pH 6.7 to pH 10.0;        -   (b) determining the antigen-binding activity of the            antigen-binding molecule at pH 4.0 to pH 6.5; and        -   (c) selecting an antigen-binding molecule whose            antigen-binding activity at pH 6.7 to pH 10.0 is greater            than the antigen-binding activity at pH 4.0 to pH 6.5;    -   [29] the screening method of [28], which comprises the step of        selecting an antibody whose antigen-binding activity at pH 6.7        to pH 10.0 is twice or higher that of the antigen-binding        activity at pH 4.0 to pH 6.5;    -   [30] a method of screening for an antigen-binding molecule,        which comprises the steps of:        -   (a) binding an antigen-binding molecule to an antigen under            a condition of pH 6.7 to pH 10.0;        -   (b) placing the antigen-binding molecule that bound to the            antigen of (a) under a condition of pH 4.0 to pH 6.5; and        -   (c) obtaining an antigen-binding molecule that dissociated            under the condition of pH 4.0 to pH 6.5;    -   [31] a method of screening for an antigen-binding molecule whose        binding activity at a first pH is greater than that at a second        pH, which comprises the steps of:        -   (a) binding an antigen-binding molecule to an            antigen-immobilized column under the condition of a first            pH;        -   (b) eluting the antigen-binding molecule that had bound to            the column at the first pH from the column under the            condition of a second pH; and        -   (c) collecting the eluted antigen-binding molecule;    -   [32] a method of screening for an antigen-binding molecule whose        binding activity at a first pH is greater than that at a second        pH, which comprises the steps of:        -   (a) binding an antigen-binding molecule library to an            antigen-immobilized column under the condition of a first            pH;        -   (b) eluting the antigen-binding molecule from the column            under the condition of a second pH;        -   (c) amplifying the gene encoding the eluted antigen-binding            molecule; and        -   (d) obtaining the eluted antigen-binding molecule.    -   [33] the screening method of [31] or [32], wherein the first pH        is 6.7 to 10.0 and the second pH is 4.0 to 6.5;    -   [34] the screening method of any one of [28] to [33], wherein at        least one or more amino acids of the antigen-binding molecule        has been substituted with histidine, or at least one histidine        has been inserted into the antigen-binding molecule;    -   [35] the screening method of any one of [28] to [33], for        obtaining an antigen-binding molecule that is superior in        retention in the plasma;    -   [36] the screening method of any one of [28] to [33], for        obtaining an antigen-binding molecule that is capable of binding        to an antigen two or more times;    -   [37] the screening method of any one of [28] to [33], for        obtaining an antigen-binding molecule that is capable of binding        to more antigens as compared to the number of its        antigen-binding sites;    -   [38] the screening method of any one of [28] to [33], for        obtaining an antigen-binding molecule that dissociates an        extracellularly-bound antigen within a cell.    -   [39] the screening method of any one of [28] to [33], for        obtaining an antigen-binding molecule that is bound to an        antigen and internalized into a cell, and released to the        outside of the cell in an antigen-free form;    -   [40] the screening method of any one of [28] to [33], for        obtaining an antigen-binding molecule that has increased ability        to eliminate an antigen in plasma;    -   [41] the screening method of any one of [28] to [40], wherein        the antigen-binding molecule is used as a pharmaceutical        composition;    -   [42] the screening method of any one of [28] to [41], wherein        the antigen-binding molecule is an antibody;    -   [43] a method for producing an antigen-binding molecule, which        comprises the steps of:        -   (a) determining the antigen-binding activity of an            antigen-binding molecule at pH 6.7 to pH 10.0;        -   (b) determining the antigen-binding activity of the            antigen-binding molecule at pH 4.0 to pH 6.5;        -   (c) selecting the antigen-binding molecule whose            antigen-binding activity at pH 6.7 to pH 10.0 is greater            than that at pH 4.0 to pH 6.5;        -   (d) obtaining the gene encoding the antigen-binding molecule            selected in (c); and        -   (e) producing the antigen-binding molecule using the gene            obtained in (d);    -   [44] a method for producing an antigen-binding molecule, which        comprises the steps of:        -   (a) binding an antigen-binding molecule to an antigen under            a condition of pH 6.7 to pH 10.0;        -   (b) allowing the antigen-binding molecule bound to the            antigen of (a) to stand under a condition of pH 4.0 to pH            6.5;        -   (c) collecting the antigen-binding molecule that dissociated            under the condition of pH 4.0 to pH 6.5;        -   (d) obtaining the gene encoding the antigen-binding molecule            obtained in (c); and        -   (e) producing the antigen-binding molecule using the gene            obtained in (d);    -   [45] a method for producing an antigen-binding molecule whose        binding activity at a first pH is greater than that at a second        pH, which comprises the steps of:        -   (a) binding an antigen-binding molecule to an            antigen-immobilized column under the first pH condition;        -   (b) eluting the antigen-binding molecule, which is bound to            the column at the first pH, from the column under a second            pH condition;        -   (c) collecting the eluted antigen-binding molecule;        -   (d) obtaining the gene encoding the antigen-binding molecule            obtained in (c); and        -   (e) producing the antigen-binding molecule using the gene            obtained in (d);    -   [46] a method for producing an antigen-binding molecule whose        binding activity at a first pH is greater than that at a second        pH, which comprises the steps of:        -   (a) binding an antigen-binding molecule library to an            antigen-immobilized column under the first pH condition;        -   (b) eluting the antigen-binding molecule from the column            under the second pH condition;        -   (c) amplifying the gene encoding the eluted antigen-binding            molecule;        -   (d) collecting the eluted antigen-binding molecule;        -   (e) obtaining the gene encoding the antigen-binding molecule            collected in (d); and        -   (f) producing the antigen-binding molecule using the gene            obtained in (e);    -   [47] the production method of [45] or [46], wherein the first pH        is 6.7 to 10.0 and the second pH is 4.0 to 6.5.    -   [48] the production method of any one of [43] to [47], which        further comprises the step of substituting at least one amino        acid of the antigen-binding molecule with histidine, or        inserting at least one histidine into the antigen-binding        molecule;    -   [49] the production method of any one of [43] to [48], wherein        the antigen-binding molecule is an antibody;    -   [50] a pharmaceutical composition comprising an antigen-binding        molecule produced by the production method of any one of [43] to        [49].

Effects of the Invention

The present invention provides methods for making single antigen-bindingmolecules to repeatedly bind to multiple antigen molecules. When anantigen-binding molecule binds to multiple antigen molecules, thepharmacokinetics of the antigen-binding molecule can be improved andsuch molecule can exert more superior in vivo effects than those ofordinary antigen-binding molecules.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram depicting a degradation pathway of antibodies boundto membrane-bound antigen.

FIG. 2 is a diagram depicting a mechanism by which IgG molecules aresalvaged by FcRn.

FIG. 3 is a schematic diagram depicting the re-binding of IgG moleculesto new antigen following dissociation from membrane-bound antigen withinendosomes.

FIG. 4 is a schematic diagram depicting the re-binding of IgG moleculesto new antigen following dissociation from soluble antigen withinendosomes.

FIG. 5 is a diagram depicting the process of panning using anantigen-immobilized column.

FIG. 6 presents graphs depicting the results of phage ELISA for clonesacquired by column panning. The upper graph depicts WT and the lowergraph depicts CL5.

FIG. 7 is a graph depicting the biological neutralization activity ofpH-dependently-binding anti-IL-6 receptor antibodies.

FIG. 8 presents Biacore™ sensorgrams depicting binding ofpH-dependently-binding anti-IL-6 receptor antibodies to soluble IL-6receptor at pH 7.4. The top graph depicts WT; the second graph from thetop depicts H3pI/L73; the third graph from the top depicts H170/L82; andthe bottom graph depicts CLH5/L73.

FIG. 9 presents Biacore™ sensorgrams depicting binding ofpH-dependently-binding anti-IL-6 receptor antibodies to soluble IL-6receptor at pH 5.8. The top graph depicts WT; the second graph from thetop depicts H3pI/L73; the third graph from the top depicts H170/L82; andthe bottom graph depicts CLH5/L73.

FIG. 10 presents Biacore™ sensorgrams depicting association (pH 7.4) anddissociation (pH 5.8) of pH-dependently-binding anti-IL-6 receptorantibodies to membrane-type IL-6 receptor. The top graph depicts WT; thesecond graph from the top depicts H3pI/L73; the third graph from the topdepicts H170/L82; and the bottom graph depicts CLH5/L73.

FIG. 11 is a Biacore™ sensorgram indicating repeated binding ofpH-dependently-binding anti-IL-6 receptor antibodies to SR344.

FIG. 12 is a graph depicting the total amount of bound antigen in arepetitive binding experiment of pH-dependently-binding anti-IL-6receptor antibodies to SR344.

FIG. 13 is a graph depicting time courses of antibody plasmaconcentrations of pH-dependently-binding anti-IL-6 receptor antibodiesin human IL-6 receptor transgenic mice.

FIG. 14 is a graph depicting time courses of antibody plasmaconcentrations of pH-dependently-binding anti-IL-6 receptor antibodiesin cynomolgus monkeys.

FIG. 15 is a graph depicting time courses of CRP concentrations incynomolgus monkeys, in relation to pH-dependently-binding anti-IL-6receptor antibodies.

FIG. 16 is a graph depicting time courses of unbound-type cynomolgusmonkey IL-6 receptor concentrations in cynomolgus monkeys, in relationto pH-dependently-binding anti-IL-6 receptor antibodies.

FIG. 17 presents Biacore™ sensorgrams depicting association (pH 7.4) anddissociation (pH 5.8) of pH-dependently-binding anti-IL-6 receptorantibodies to membrane-type IL-6 receptor. In order moving from the top,the results for WT, H3pI/L73-IgG1, Fv2-IgG1, and Fv4-IgG1 are shown.

FIG. 18 is a graph depicting time courses of plasma antibodyconcentrations of pH-dependently-binding anti-IL-6 receptor antibodies(WT, H3pI/L73-IgG1, Fv2-IgG1, and Fv4-IgG1) in human IL-6 receptortransgenic mice.

FIG. 19 presents Biacore™ sensorgrams depicting association (pH 7.4) anddissociation (pH 5.8) of pH-dependently-binding anti-IL-6 receptorantibodies to membrane-type IL-6 receptor. Moving from the top down, theresults for WT, Fv4-IgG1, Fv4-IgG2, and Fv4-M58 are shown.

FIG. 20 is a graph showing time courses of antibody plasmaconcentrations of pH-dependently-binding anti-IL-6 receptor antibodies(WT, Fv4-IgG1, Fv4-IgG2, and Fv4-M58) in human IL-6 receptor transgenicmice.

FIG. 21 presents Biacore™ sensorgrams depicting association (pH 7.4) anddissociation (pH 5.8) of pH-dependently-binding anti-IL-6 receptorantibodies to membrane-type IL-6 receptor. Moving from the top down, theresults for Fv1-M71, Fv1-M73, Fv3-M71, and Fv3-M73 are shown.

FIG. 22 is a graph depicting time courses of antibody plasmaconcentrations of pH-dependently-binding anti-IL-6 receptor antibodiesin cynomolgus monkeys, during administration of H3pI/L73-IgG1, Fv1-M71,Fv1-M73, Fv2-IgG1, Fv3-M73, and Fv4-M73 at 0.5 mg/kg and duringadministration of high affinity Ab at 1.0 mg/kg.

FIG. 23 is a graph depicting time courses of CRP concentrations incynomolgus monkeys, in relation to pH-dependently-binding anti-IL-6receptor antibodies (H3pI/L73-IgG1-, Fv1-M71-, Fv1-M73-, Fv2-IgG1-,Fv3-M73-, Fv4-M73-, and high-affinity-Ab-administered groups).

FIG. 24 is a graph depicting time courses of unbound-type cynomolgusmonkey IL-6 receptor concentrations in cynomolgus monkeys, in relationto pH-dependently-binding anti-IL-6 receptor antibodies (H3pI/L73-IgG1-,Fv1-M71-, Fv1-M73-, Fv2-IgG1-, Fv3-M73-, Fv4-M73-, andhigh-affinity-Ab-administered groups).

FIG. 25 is a diagram depicting FR1, FR2, FR3, and FR4 along with CDR1,CDR2, and CDR3 of heavy chains (VH1, VH2, VH3, VH4) and light chains(VL1, VL2, VL3). Asterisks indicate locations where amino acid mutationsexist in the aligned sequences.

FIG. 26 presents Biacore™ sensorgrams depicting the pH-dependent bindingof an anti-IL-6 antibody, Anti-IL6 clone 2, to IL-6 at pH 7.4 and pH5.5. The curves in the sensorgram at pH 7.4 correspond to 100, 50, 25,12.5, and 6.25 ng/mL IL-6, from above.

FIG. 27 presents Biacore™ sensorgrams depicting the pH-dependent bindingof an anti-IL-31 receptor antibody, Anti-IL31R clone 1, to the IL-31receptor at pH 7.4 and pH 5.5. The curves in the sensorgram at pH 5.5correspond to 100, 50, 25, and 12.5 ng/mL IL-31 receptor, from above.

FIG. 28 depicts the time course of plasma antibody concentration afterintravenous administration of a mixture solution containing SR344 and ananti-human IL-6 receptor antibody to mouse.

FIG. 29 depicts the time course of plasma SR344 concentration afterintravenous administration of a mixture solution containing SR344 and ananti-human IL-6 receptor antibody to mouse.

MODE FOR CARRYING OUT THE INVENTION

The present invention provides methods for increasing the number oftimes of antigen-binding in antigen-binding molecules. Morespecifically, the present invention provides methods for increasing thenumber of times of antigen-binding in antigen-binding molecules byimpairing the antigen-binding ability of the antigen-binding moleculesat acidic pH as compared to that at neutral pH. Furthermore, the presentinvention provides methods for increasing the number of times ofantigen-binding in antigen-binding molecules by substituting histidinefor at least one amino acid in the antigen-binding molecules orinserting at least one histidine into the antigen-binding molecules. Inaddition, the present invention provides methods for increasing thenumber of times of antigen-binding in antigen-binding molecules bysubstituting, deleting, adding, and/or inserting amino acids in theantibody constant region of antigen-binding molecules.

The present invention also provides methods for increasing the number ofantigens that can be bound by an antigen-binding molecule. Morespecifically, the present invention provides methods for increasing thenumber of antigens that can be bound by an antigen-binding molecule byimpairing the antigen-binding ability at acidic pH as compared to thatat neutral pH. Furthermore, the present invention provides methods forincreasing the number of antigens that can be bound by anantigen-binding molecule by substituting histidine for at least oneamino acid in the antigen-binding molecules or inserting at least onehistidine into the antigen-binding molecules. In addition, the presentinvention provides methods for increasing the number of antigens thatcan be bound by an antigen-binding molecule through substituting,deleting, adding, and/or inserting amino acids in the antibody constantregion of antigen-binding molecules.

The present invention also provides methods for dissociating within acell an antigen from an extracellularly-bound antigen-binding molecule.More specifically, the present invention provides methods fordissociating within a cell an antigen from an extracellularly-boundantigen-binding molecule by impairing the antigen-binding ability atacidic pH as compared to that at neutral pH. Furthermore, the presentinvention provides methods for dissociating within a cell an antigenfrom an extracellularly-bound antigen-binding molecule by substitutinghistidine for at least one amino acid in the antigen-binding molecule orinserting at least one histidine into the antigen-binding molecule. Inaddition, the present invention provides methods for dissociating withina cell an antigen from an extracellularly-bound antigen-binding moleculethrough substituting, deleting, adding, and/or inserting amino acids inthe antibody constant region of antigen-binding molecule.

The present invention also provides methods for releasing anantigen-binding molecule, which has been bound to an antigen andinternalized into a cell, in an antigen-free form to the outside of thecell. More specifically, the present invention provides methods forreleasing an antigen-binding molecule, which has been bound to anantigen and internalized into a cell, in an antigen-free form to theoutside of the cell, by impairing the antigen-binding ability at acidicpH as compared to that at neutral pH. Furthermore, the present inventionprovides methods for releasing an antigen-binding molecule, which hasbeen bound to an antigen and internalized into a cell, in anantigen-free form to the outside of the cell, by substituting histidinefor at least one amino acid in the antigen-binding molecule or insertingat least one histidine into the antigen-binding molecule. In addition,the present invention provides methods for releasing an antigen-bindingmolecule, which has been bound to an antigen and internalized into acell, in an antigen-free form to the outside of the cell, throughsubstituting, deleting, adding, and/or inserting amino acids in theantibody constant region of antigen-binding molecule.

The present invention also provides methods for increasing the abilityof an antigen-binding molecule to eliminate antigens in plasma. Morespecifically, the present invention provides methods for increasing theability of an antigen-binding molecule to eliminate antigens in plasmaby impairing the antigen-binding ability at acidic pH as compared tothat at neutral pH. Furthermore, the present invention provides methodsfor increasing the ability of an antigen-binding molecule to eliminateantigens in plasma by substituting histidine for at least one amino acidin the antigen-binding molecules or inserting at least one histidineinto the antigen-binding molecules. In addition, the present inventionprovides methods for increasing the ability of an antigen-bindingmolecule to eliminate antigens in plasma through substituting, deleting,adding, and/or inserting amino acids in the antibody constant region ofantigen-binding molecule.

The present invention also provides methods for improving thepharmacokinetics of antigen-binding molecules. More specifically, thepresent invention provides methods for improving the pharmacokinetics ofantigen-binding molecules (prolonging the retention in plasma) byimpairing the antigen-binding ability at acidic pH as compared to thatat neutral pH. Furthermore, the present invention provides methods forimproving the pharmacokinetics of antigen-binding molecules bysubstituting histidine for at least one amino acid in theantigen-binding molecules or inserting at least one histidine into theantigen-binding molecules. In addition, the present invention providesmethods for improving the pharmacokinetics of antigen-binding moleculesby substituting, deleting, adding, and/or inserting amino acids in theantibody constant region of antigen-binding molecules.

Further, the present invention provides methods for increasing theability of the antigen-binding molecules to eliminate antigens inplasma. More specifically, the present invention provides methods forincreasing the ability of the antigen-binding molecules to eliminateantigens in plasma by impairing the antigen-binding ability of theantigen-binding molecules at acidic pH as compared to that at neutralpH. Furthermore, the present invention provides methods for increasingthe ability of the antigen-binding molecules to eliminate antigens inplasma by substituting at least one amino acid in the antigen-bindingmolecules with histidine or inserting at least one histidine into theantigen-binding molecules. In addition, the present invention providesmethods for increasing the ability of the antigen-binding molecules toeliminate antigens in plasma by substituting, deleting, adding, and/orinserting amino acids in the antibody constant region of antigen-bindingmolecules.

Herein, “improvement of the pharmacokinetics”, “amelioration of thepharmacokinetics”, “superior pharmacokinetics” are interchangeable with“improvement of the retention in plasma (blood)”, “amelioration of theretention in plasma (blood)”, and “superior retention in plasma(blood)”, respectively, and these phrases are synonymous.

Herein, impairing the antigen-binding activity at acidic pH as comparedto that at neutral pH means that the antigen-binding ability of anantigen-binding molecule at pH 4.0 to pH 6.5 is impaired as compared tothat at pH 6.7 to pH 10.0, preferably that the antigen-binding activityof an antigen-binding molecule at pH 5.5 to pH 6.5 is impaired ascompared to that at pH 7.0 to pH 8.0, and more preferably that theantigen-binding activity of an antigen-binding molecule at pH 5.8 isimpaired as compared to that at pH 7.4. Accordingly, in the presentinvention, acidic pH is typically pH 4.0 to pH 6.5, preferably pH 5.5 topH 6.5, and more preferably pH 5.8. Alternatively, in the presentinvention, neutral pH is typically pH 6.7 to pH 10.0, preferably pH 7.0to pH 8.0, and more preferably pH 7.4.

Herein, the phrase “impairing the antigen-binding ability of anantigen-binding molecule at acidic pH as compared to that at neutral pH”is interchangable with the phrase “increasing the antigen-bindingability of an antigen-binding molecule at neutral pH as compared to thatat acidic pH”. In other words, in the present invention, the differencein the antigen-binding ability of an antigen-binding molecule should beincreased between acidic and neutral pHs. For example, the value ofKD(pH5.8)/KD(pH7.4) should be increased, as described below. Thedifference in the antigen-binding ability of an antigen-binding moleculebetween acidic and neutral pHs may be increased, for example, by eitheror both, impairing the antigen-binding ability at acidic pH andincreasing the antigen-binding ability at neutral pH.

Conditions other than the pH for determining the antigen-bindingactivity can be selected appropriately by those skilled in the art, andthe conditions are not particularly limited. The antigen-bindingactivity can be determined, for example, under conditions of MES bufferand 37° C. as described in the Examples herein. Furthermore, theantigen-binding activity of an antigen-binding molecule can bedetermined by methods known to those skilled in the art, for example,using a Biacore™ surface plasmon resonance system (GE Healthcare) or thelike, as described in the Examples herein. When the antigen is a solubleantigen, the activity of binding to the soluble antigen can be assessedby injecting the antigen as an analyte onto a chip immobilized with theantigen-binding molecule. Alternatively, when the antigen is a membraneantigen, the activity of binding to the membrane antigen can be assessedby injecting the antigen-binding molecule as an analyte onto anantigen-immobilized chip.

In the present invention, the difference in the antigen-binding activitybetween acidic and neutral pHs is not particularly limited as long asthe antigen-binding activity at acidic pH is lower than that at neutralpH. However, the value of KD(pH5.8)/KD(pH7.4), which is a ratio ofdissociation constant (KD) against an antigen at pH 5.8 and that at pH7.4, is preferably 2 or greater, more preferably 10 or greater, andstill more preferably 40 or greater. The upper limit ofKD(pH5.8)/KD(pH7.4) value is not particularly limited, and may be anyvalue, for example, 400, 1,000, or 10,000, as long as the molecule canbe produced by technologies of those skilled in the art. When theantigen is a soluble antigen, the antigen-binding activity can bepresented in terms of the dissociation constant (KD). Alternatively,when the antigen is a membrane antigen, the antigen-binding activity canbe presented in terms of the apparent dissociation constant. Thedissociation constant (KD) and apparent dissociation constant (apparentKD) can be determined by methods known to those skilled in the art, forexample, using a Biacore™ surface plasmon resonance system (GEHealthcare), Scatchard plot, or FACS.

Alternatively, it is possible to use, for example, kd, a dissociationrate constant, as an indicator for the difference in the antigen-bindingactivity between acidic and neutral pHs. When the dissociation rateconstant (kd) is used as an indicator for the difference in the bindingactivity instead of the dissociation constant (KD), the value ofkd(pH5.8)/kd(pH7.4), which is a ratio of dissociation rate constant (kd)against an antigen at pH 5.8 and that at pH 7.4, is preferably 2 orgreater, more preferably 5 or greater, even more preferably 10 orgreater, and still more preferably 30 or greater. The upper limit ofkd(pH5.8)/kd(pH7.4) value is not particularly limited, and may be anyvalue, for example, 50, 100, or 200, as long as the molecule can beproduced by technologies common to those skilled in the art.

When the antigen is a soluble antigen, the antigen-binding activity canbe presented in terms of the dissociation rate constant (kd).Alternatively, when the antigen is a membrane antigen, theantigen-binding activity can be presented in terms of the apparentdissociation rate constant. The dissociation rate constant (kd) andapparent dissociation rate constant (apparent kd) can be determined bymethods known to those skilled in the art, for example, using a Biacore™surface plasmon resonance system (GE Healthcare) or FACS.

In the present invention, when the antigen-binding activity of anantigen-binding molecule is determined at different pHs, it is preferredthat the measurement conditions except for pH are constant.

The methods for impairing the antigen-binding activity of anantigen-binding molecule at pH 5.8 as compared to that at pH 7.4(methods for conferring the pH-dependent binding ability) are notparticularly limited and may be any methods. Such methods include, forexample, methods for impairing the antigen-binding activity at pH 5.8 ascompared to that at pH 7.4 by substituting histidine for amino acids inthe antigen-binding molecule or inserting histidine into theantigen-binding molecule. It is already known that an antibody can beconferred with a pH-dependent antigen-binding activity by substitutinghistidine for amino acids in the antibody (FEBS Letter, 309(1), 8588(1992)). Such histidine mutation (substitution) or insertion sites arenot particularly limited, and any site is acceptable as long as theantigen-binding activity at pH 5.8 is lowered than that at pH 7.4 (thevalue of KD(pH5.8)/KD(pH7.4) gets greater) as compared to beforemutation or insertion. When the antigen-binding molecule is an antibody,such sites include, for example, sites within an antibody variableregion. The appropriate number of histidine mutation or insertion sitescan be appropriately determined by those skilled in the art. Histidinemay be substituted or inserted at a single site, or two or more sites.It is also possible to introduce non-histidine mutation (mutation withamino acids other than histidine) at the same time. Furthermore,histidine mutation may be introduced simultaneously with histidineinsertion. It is possible to substitute or insert histidine at randomusing a method such as histidine scanning, which uses histidine insteadof alanine in alanine scanning known to those skilled in the art.Alternatively, antigen-binding molecules whose KD(pH5.8)/KD(pH7.4) isincreased as compared to before mutation can be selected from anantigen-binding molecule library with random histidine mutation orinsertion.

When histidine is substituted for amino acids of an antigen-bindingmolecule or inserted between amino acids of the molecule, it ispreferred, but not required, that the antigen-binding activity of theantigen-binding molecule at pH 7.4 after histidine substitution orinsertion is comparable to that at pH 7.4 before histidine substitutionor insertion. The “antigen-binding activity of the antigen-bindingmolecule at pH 7.4 after histidine substitution or insertion iscomparable to that at pH 7.4 before histidine substitution or insertion”means that even after histidine substitution or insertion, theantigen-binding molecule retains 10% or more, preferably 50% or more,more preferably 80% or more, and still more preferably 90% or more ofthe antigen-binding activity of before histidine substitution orinsertion. When the antigen-binding activity of the antigen-bindingmolecule has been impaired due to histidine substitution or insertion,the antigen-binding activity may be adjusted by introducingsubstitution, deletion, addition, and/or insertion of one or more aminoacids into the antigen-binding molecule so that the antigen-bindingactivity becomes comparable to that before histidine substitution orinsertion. The present invention also includes such antigen-bindingmolecules having a comparable binding activity as a result ofsubstitution, deletion, addition, and/or insertion of one or more aminoacids after histidine substitution or insertion.

Alternative methods for impairing the antigen-binding activity of anantigen-binding molecule at pH 5.8 as compared to that at pH 7.4 includemethods of substituting non-natural amino acids for amino acids in anantigen-binding molecule or inserting non-natural amino acids into aminoacids of an antigen-binding molecule. It is known that the pKa can beartificially controlled using non-natural amino acids (Angew. Chem. Int.Ed. 2005, 44, 34; Chem Soc Rev. 2004 Sep. 10; 33(7):422-30; Amino Acids.1999; 16(3-4):345-79). Thus, in the present invention, non-natural aminoacids can be used instead of histidine described above. Such non-naturalamino acid substitution and/or insertion may be introducedsimultaneously with the histidine substitution and/or insertiondescribed above. Any non-natural amino acids may be used in the presentinvention. It is possible to use non-natural amino acids known to thoseskilled in the art.

Furthermore, when the antigen-binding molecule is a substance having anantibody constant region, alternative methods for impairing theantigen-binding activity of the antigen-binding molecule at pH 5.8 ascompared to that at pH 7.4 include methods for modifying the antibodyconstant region contained in the antigen-binding molecule. Such methodsfor modifying the antibody constant region include, for example, methodsfor substituting a constant region described in the Examples herein.

Alternative methods for modifying the antibody constant region include,for example, methods to assess various constant region isotypes (IgG1,IgG2, IgG3, and IgG4) and select an isotype that impairs theantigen-binding activity at pH 5.8 (increases the dissociation rate atpH 5.8). Alternatively, methods include those for impairing theantigen-binding activity at pH 5.8 (increasing the dissociation rate atpH 5.8) by substituting amino acids in the amino acid sequence of awild-type isotype (the amino acid sequence of wild type IgG1, IgG2,IgG3, or IgG4). The sequence of the hinge region of an antibody constantregion is considerably different among isotypes (IgG1, IgG2, IgG3, andIgG4), and the difference in the hinge region amino acid sequence has agreat impact on the antigen-binding activity. Thus, it is possible toselect an appropriate isotype to impair the antigen-binding activity atpH 5.8 (to increase the dissociation rate at pH 5.8) by considering thetype of antigen or epitope. Furthermore, since the difference in thehinge region amino acid sequence has a significant influence on theantigen-binding activity, preferred amino acid substitution sites in theamino acid sequence of a wild type isotype are assumed to be within thehinge region.

When the antigen-binding activity of the antigen-binding substance at pH5.8 is weakened compared to that at pH 7.4 (when KD(pH5.8)/KD(pH7.4)value is increased) by the above described methods and such, it isgenerally preferable that the KD(pH5.8)/KD(pH7.4) value be two times ormore, more preferably five times or more, and even more preferably tentimes or more as compared to that of the original antibody, although theinvention is not particularly limited thereto.

Herein, the “improvement of the pharmacokinetics” means prolongation ofthe time required for the elimination of the antigen-binding moleculefrom plasma (for example, reaching the state where the antigen-bindingmolecule cannot return to the plasma due to degradation in cells, orother reasons) after administration to an animal such as human, mouse,rat, monkey, rabbit, or dog, as well as prolongation of the plasmaretention time of the antigen-binding molecule being in a form capableof binding to antigens (for example, being in an antigen-free form)during the period until it is eliminated from the plasma afteradministration. Even if an antigen-binding molecule is circulated inplasma, it cannot bind to an antigen when it already binds to anotherantigen. Accordingly, the period where the antigen-binding molecule cannewly binds to another antigen is prolonged (the chance to bind anotherantigen increases) by prolonging the period where the antigen-bindingmolecule is in an antigen-free form. This makes it possible to shortenthe period where the antigen is free from antigen-binding molecules invivo (in other words, to prolong the period where the antigen is boundby an antigen-binding molecule). For example, the ratio of antigensbound to antigen-binding molecules against the antigens in the body inplasma (total of antigen molecules bound to and free from theantigen-binding molecules) generally decreases in a certain period oftime after the administration of the antigen-binding molecules. However,such decrease can be suppressed (for example, the degree of decrease canbe made smaller) by prolonging the retention time of the antigen-bindingmolecules in a form capable of binding to antigens. This results in anincrease in the ratio of antigens bound to antigen-binding moleculesagainst the antigens in the body in a certain period of time afterantibody administration.

Specifically, in the present invention, the “improvement of thepharmacokinetics” does not necessarily mean the prolongation (extension)of the time required for the elimination of the antigen-binding moleculeafter administration. Even if the time required for the elimination ofthe antigen-binding molecule after administration remains unchanged, thepharmacokinetics can be said “improved” in the present invention if theplasma retention time of the antigen-binding molecule being in a formcapable of binding to an antigen (for example, the antigen-bindingmolecule being in an antigen-free form) is prolonged;

the period where the antigen is free from an antigen-binding molecule inthe body is shortened (in other words, the period where theantigen-binding molecule is bound to an antigen is prolonged); and theratio of antigens bound to antigen-binding molecules against theantigens in the body is increased. Thus, in the present invention, the“improvement of the pharmacokinetics” encompasses at least:

-   -   (1) prolongation of the time required for the elimination of the        antigen-binding molecule from plasma after administration of the        antigen-binding molecule;    -   (2) prolongation of the plasma retention time of the        antigen-binding molecule in a form capable of binding to an        antigen after administration of the antigen-binding molecule;    -   (3) shortening of the period where the antigen is free from an        antigen-binding molecule in the body after administration of the        antigen-binding molecule (prolongation of the period where the        antigen-binding molecule is bound to an antigen in the body);        and    -   (4) increase in the ratio of antigens bound to antigen-binding        molecules to the antigen in the body.

When the antigen is a soluble antigen present in plasma, even if thepharmacokinetics of the antigen-binding molecule (rate of eliminationfrom plasma) is equivalent, there are cases where elimination of antigenbound to the antigen-binding molecule is accelerated. Reducing thepharmacokinetics of the antigen (accelerating elimination from plasma)results in the relative improvement of the pharmacokinetics of theantigen-binding molecule, and thus, leads to the prolongation of thetime of the antigen-binding molecule present in plasma in a form capableof binding to antigens. Thus, in one embodiment, the “improvement of thepharmacokinetics” of antigen-binding molecules of the present inventionincludes increasing the rate of eliminating soluble antigens from plasmaafter administration of the antigen-binding molecules (the ability ofthe antigen-binding molecule to eliminate antigens from plasma).

In the present invention, when the antigen is a membrane antigen,whether a single antigen-binding molecule binds to multiple antigens canbe assessed by testing whether the pharmacokinetics of theantigen-binding molecule is improved. Whether the “pharmacokinetics isimproved” can be assessed by the following method. For example, whetherthe time required for the elimination of an antigen-binding moleculeafter administration is prolonged can be assessed by determining any oneof parameters for the antigen-binding molecule, such as half-life inplasma, mean plasma retention time, and clearance in plasma(“Pharmacokinetics: Enshu-niyoru Rikai (Understanding through practice)”Nanzando). For example, when the half-life in plasma or mean plasmaretention time of an antigen-binding molecule administered to mice,rats, monkeys, rabbits, dogs, humans, or other animals is prolonged, thepharmacokinetics of the antigen-binding molecule is judged to beimproved. These parameters can be determined by methods known to thoseskilled in the art. For example, the parameters can be appropriatelyassessed by noncompartmental analysis using pharmacokinetics analysissoftware WinNonlin (Pharsight) according to the appended instructionmanual.

Alternatively, whether the plasma retention time of an antigen-bindingmolecule in a form capable of binding to antigens after administrationof the antigen-binding molecule is prolonged can be assessed bymeasuring the plasma concentration of the antigen-free antigen-bindingmolecule and determining any one of parameters for the antigen-freeantigen-binding molecule, such as half-life in plasma, mean plasmaretention time, and clearance in plasma. The concentration of theantigen-free antigen-binding molecule in plasma can be measured bymethods known to those skilled in the art. For example, suchmeasurements are described in Clin Pharmacol. 2008 April; 48(4):406-17.

Furthermore, whether the period where an antigen is free from theantigen-binding molecules in the body after administration of theantigen-binding molecules is shortened (the period where theantigen-binding molecule is bound to an antigen in the body isprolonged) can be assessed by determining the plasma concentration ofthe unbound antigen that is free from antigen-binding molecules, andconsidering the period where the concentration of free antigen in plasmor the amount ratio of free antigen against the total antigen remainslow. The plasma concentration of the free antigen or amount ratio offree antigen against total antigen can be determined by methods known tothose skilled in the art. For example, such measurements are describedin Pharm Res. 2006 January; 23(1):95-103. Alternatively, when theantigen exerts some function in vivo, whether the antigen is bound by anantigen-binding molecule that neutralizes the antigen's function(antagonistic molecule) can be assessed by testing whether the functionof the antigen is neutralized. Whether the function of the antigen isneutralized can be assessed by assaying an in vivo marker that reflectsthe function of the antigen. Whether the antigen is bound by anantigen-binding molecule that activates the function of the antigen(agonistic molecule) can be assessed by assaying an in vivo marker thatreflects the function of the antigen.

There is no particular limitation on the determination of the plasmaconcentration of free antigen and amount ratio of free antigen againsttotal antigen, and in vivo marker assay, but the determination ispreferably carried out after a certain period following administrationof an antigen-binding substance. In the present invention, such a periodfollowing administration of an antigen-binding substance is notparticularly limited, and an appropriate period can be determined bythose skilled in the art depending on the properties of the administeredantigen-binding substance and the like. Examples of the period are: oneday after administration of an antigen-binding substance; three daysafter administration of an antigen-binding substance, seven days afteradministration of an antigen-binding substance, 14 days afteradministration of an antigen-binding substance, and 28 days afteradministration of an antigen-binding substance.

In the present invention, it is preferred to improve thepharmacokinetics in human. Even when the plasma retention in human isdifficult to determine, it can be predicted based on the plasmaretention in mice (for example, normal mice, human antigen-expressingtransgenic mice, and human FcRn-expressing transgenic mice) or monkeys(for example, cynomolgus monkeys).

Methods for determining the retention in plasma are not particularlylimited. The determination can be carried out, for example, according tothe methods described in the Examples herein.

Whether an antigen-binding molecule is capable of binding to antigensmultiple times can be assessed by testing whether the antigen bound toan antigen-binding molecule under the same neutral condition as plasmadissociates under the same acidic condition as endosome and how manyantigens the antigen-binding molecule can rebind to under the neutralcondition. Specifically, the assessment can be carried out by allowingthe antigen-binding molecule and antigen to form a complex under theneutral condition, exposing the complex to an acidic condition for apredetermined period, and then testing whether the antigen-bindingmolecule can rebind to an antigen under the neutral condition, using adevice for assaying antigen-binding molecule-antigen reactions, such asa Biacore™ surface plasmon resonance system. When the antigen-bindingcapacity of the antigen-binding molecule conferred with the pH-dependentbinding ability has been improved to twice that of the antigen-bindingmolecule before modification, the number of times of binding of theantigen-binding molecule conferred with the pH-dependent binding abilitycan be judged to be increased to twice that of the antigen-bindingmolecule before modification. Alternatively, when the antigen is amembrane antigen and thus the antigen-binding molecule is eliminatedfrom plasma through antigen-mediated uptake and degradation in alysosome, whether the number of times of binding of the antigen-bindingmolecule conferred with the pH-dependent binding ability is increased ascompared to that before modification can be assessed by comparing thepharmacokinetics or duration of antigen binding between theantigen-binding molecule conferred with the pH-dependent binding abilityand the antigen-binding molecule before modification. For example, whenthe antigen-binding duration of the antigen-binding molecule conferredwith the pH-dependent binding ability is prolonged twice that of theantigen-binding molecule before modification, the number of times ofbinding of the antigen-binding molecule conferred with the pH-dependentbinding ability is judged to be increased to twice that of theantigen-binding molecule before modification. Alternatively, when theplasma concentration of an unbound antigen, which is free from theantigen-binding molecule, is determined and the period where the plasmaconcentration of the free antigen or the amount ratio of the freeantigen against the total antigen remains low is prolonged to twice, thenumber of times of binding of the antigen-binding molecule conferredwith the pH-dependent binding ability is judged to be increased to twicethat of the antigen-binding molecule before modification.

When the antigen is a soluble antigen, if the antigen bound to anantigen-binding molecule under the neutral condition in plasmadissociates in an endosome, and the antigen-binding molecule returns tothe plasma, the antigen-binding molecule can again bind to an antigenunder the neutral condition in plasma. Thus, an antigen-binding moleculethat has the characteristics to dissociate with an antigen in acidiccondition of an endosome is capable of binding to antigens multipletimes. Compared to when the antigen bound to an antigen-binding moleculedoes not dissociate in an endosome (the antigen remains bound to theantigen-binding molecule when returning to plasma), when the antigenbound to an antigen-binding molecule dissociates in endosomes, theantigen is delivered to a lysosome and then degraded, and thus, the rateof elimination of the antigen from plasma increases. That is, it is alsopossible to determine whether the antigen-binding molecule is capable ofbinding to antigens multiple times using the rate of elimination ofantigen from plasma as an index. The rate of elimination of the antigenfrom plasma can be determined, for example, by administering theantigens (e.g., membrane antigen) and antigen-binding molecules in vivo,and then measuring the concentration of antigens in plasma. When anantigen (e.g., membrane antigen) is produced or secreted in vivo, theplasma antigen concentration is reduced if the rate of elimination ofthe antigen from plasma is increased. Thus, it is also possible todetermine whether the antigen-binding molecule is capable of binding toantigens multiple times using the plasma antigen concentration as anindex.

Herein, “increasing the number of times of antigen-binding of theantigen-binding molecule” means that the number of cycles is increasedwhen taking as one cycle the process where an antigen-binding moleculeadministered to human, mouse, monkey, or such binds to an antigen and isinternalized into a cell. Specifically, herein, “the antigen-bindingmolecule binds twice to an antigen” means that the antigen-bindingmolecule bound by an antigen is internalized into a cell and released inan antigen-free form to the outside of the cell, and the releasedantigen-binding molecule rebinds to another antigen and is internalizedinto a cell again.

When the antigen-binding molecule is internalized into a cell, it may bein a form bound by a single antigen, or two or more antigens.

Herein, “the number of times of antigen-binding of an antigen-bindingmolecule is increased” does not necessarily mean that the number oftimes of antigen-binding increases in every antigen-binding molecules.For example, among antigen-binding molecules in anantigen-binding-molecule composition, the proportion of antigen-bindingmolecules that bind to antigens twice or more times may increase, or theaverage number of binding events of antigen-binding molecules in anantigen-binding-molecule composition may increase.

In the present invention, it is preferred that the number of times ofantigen-binding of an antigen-binding molecule increases when themolecule is administered to a human. However, when it is difficult todetermine the number of times of antigen-binding in human, the number inhuman may be predicted based on the results obtained by in vitro assayor measurement using mice (for example, antigen-expressing transgenicmice and human FcRn-expressing transgenic mice) or monkeys (for example,cynomolgus monkeys).

In the present invention, it is preferred that an antigen-bindingmolecule binds to antigens twice or more times. For example, it ispreferred that, of the antigen-binding molecules in anantigen-binding-molecule composition, at least 10% or more, preferably30% or more, more preferably 50% or more, and still more preferably 80%or more (for example, 90% or more, 95% or more, and so on) bind toantigens twice or more times.

Herein, “increasing the number of antigens that can be bound by anantigen-binding molecule” means increasing the number of antigens thatcan be bound by an antigen-binding molecule during the period until theantigen-binding molecule is degraded in a lysosome of a cell afteradministration of the antigen-binding molecule to an animal such ashuman, mouse, or monkey.

In general, antibodies such as IgG have two binding domains, and thus asingle antibody binds to a maximum of two antigens. An antibody bound toantigen(s) is internalized into a cell, and the antibody and antigen(s)are degraded in a lysosome. In general, antibodies such as IgG can bindto a maximum of two antigens. When the antigen-binding activity of anantigen-binding molecule such as an antibody at the endosomal pH isimpaired as compared to that at the plasma pH by the methods of thepresent invention, the antigen-binding molecule such as an antibodyinternalized into a cell dissociates the antigen and is released to theoutside of the cell, and thus can bind to another antigen again. Inother words, the methods of the present invention enable for anantigen-binding molecule to bind to more antigens than the number of itsantigen-binding sites. Specifically, by using the methods of the presentinvention, for example, IgG having two antigen-binding sites can bind tothree or more antigens, preferably four or more antigens, during aperiod until the antibody is degraded after administration. For example,when the antibody is a neutralizing antibody, “increasing the number ofantigens that can be bound by an antigen-binding molecule” isinterchangable with “increasing the number of antigens that theantigen-binding molecule can neutralize”. Thus, “bind” can be replacedwith “neutralize” when the antibody is a neutralizing antibody.

In the present invention, “increasing the number of antigens that can bebound by an antigen-binding molecule” does not necessarily meanincreasing the number of antigens that can be bound by everyantigen-binding molecule. For example, the average number of antigensthat can be bound by an antigen-binding molecule in anantigen-binding-molecule composition may increase, or the proportion ofantigen-binding molecules that can bind to more antigens than the numberof their antigen-binding sites may increase.

In the present invention, it is preferred that the number of antigensthat can be bound by an antigen-binding molecule increases when themolecule is administered to a human. However, when it is difficult todetermine the number in human, it may be predicted based on the resultsobtained by in vitro assay or measurement using mice (for example,antigen-expressing transgenic mice and human FcRn-expressing transgenicmice) or monkeys (for example, cynomolgus monkeys). When the antibody isa neutralizing antibody, the above-described number of times ofantigen-binding of the antigen-binding molecule is generally assumed tocorrelates with the number of antigens which can be neutralized by anantigen-binding molecule. Thus, the number of antigens which can beneutralized by an antigen-binding molecule can be determined by the samemethods described above for determining the number of times of bindingof an antigen-binding molecule.

Furthermore, the present invention provides methods for binding anantigen-binding molecule to antigens twice or more times in the body, byadministering an antigen-binding molecule whose antigen-binding activityat acidic pH is lower than that at neutral pH.

The present invention also relates to methods for neutralizing antigensthat are greater in number than the number of antigen-binding sites ofan antigen-binding molecule having the neutralizing activity, byadministering the antigen-binding molecule whose antigen-bindingactivity at acidic pH is lower than that at neutral pH. Preferably, thepresent invention relates to methods for neutralizing three or moreantigens, preferably four or more antigens by administering IgG whoseantigen-binding activity at acidic pH is lower than that at neutral pH.

The present invention also relates to methods for dissociating within acell an antigen from an extracellularly-bound antigen-binding moleculeby impairing the antigen-binding ability of the antigen-binding moleculeat acidic pH as compared to that at neutral pH. In the presentinvention, the antigen may be dissociated from the antigen-bindingmolecule anywhere within a cell; however, it is preferred that theantigen is dissociated within an early endosome. In the presentinvention, “an antigen is dissociated within a cell from anextracellularly-bound antigen-binding molecule” does not necessarilymean that every antigen internalized into a cell via binding to theantigen-binding molecule is dissociated from the antigen-bindingmolecule within the cell. It is acceptable that the proportion ofantigen that is dissociated from the antigen-binding molecule within acell increases when compared to before impairing the antigen-bindingability of the antigen-binding molecule at acidic pH as compared to thatat neutral pH.

Furthermore, the present invention relates to methods for enhancing theintracellular binding of an antigen-binding molecule free from anantigen to FcRn by impairing the antigen-binding ability of theantigen-binding molecule at acidic pH as compared to that at neutral pH.In general, FcRn binds to an antigen-binding molecule within anendosome. However, an antigen-binding molecule bound to a membraneantigen is assumed not to bind to FcRn. Thus, in a preferred embodiment,when the antigen is a membrane-bound antigen, the present inventionincludes methods for enhancing the endosomal dissociation of antigensfrom antigen-binding molecules and thus enhancing the FcRn binding ofthe antigen-binding molecules, by impairing the antigen-binding abilityof an antigen-binding molecule at the endosomal pH (acidic pH) ascompared to that at the plasma pH (neutral pH). When the antigen is asoluble antigen, the antigen-binding molecule can bind to FcRn in thepresence or absence of the antigen. If dissociation of the antigen fromthe antigen-binding molecule within endosomes can be promoted byimpairing the antigen-binding ability of the antigen-binding molecule atintraendosomal (acidic) pH as compared to that at plasma (neutral) pH,the FcRn binding of the antigen-binding molecule that is “free from anantigen” can be enhanced by the methods of the present invention.

Regardless of whether an antigen is membrane-bound or soluble, if anantigen-binding molecule free from an antigen can return to plasma withFcRn, the antigen-binding molecule can bind to the antigen again. Byrepeating this process, the antigen-binding molecule can bind to theantigen multiple times. In the present invention, “enhancing the FcRnbinding of an antigen-binding molecule within a cell” does notnecessarily mean that every antigen-binding molecule binds to FcRn. Itis acceptable that the proportion of an antigen-binding molecule freefrom an antigen that binds to FcRn within a cell increases when comparedto before impairing the antigen-binding ability of the antigen-bindingmolecule at the endosomal pH as compared to that at the plasma pH.Preferred antigen-binding molecules in the methods of the presentinvention for enhancing the intracellular binding between theantigen-binding molecule and FcRn include, for example, antigen-bindingmolecules that bind to membrane-bound antigens (membrane antigens) suchas membrane proteins. Other preferable antigen-binding molecules includeantigen-binding molecules that bind to soluble antigens such as solubleproteins.

The methods of enhancing the binding of an antigen-binding molecule andFcRn within a cell are alternatively expressed as the methods ofpromoting the FcRn binding of an antigen-binding molecule within a cell,for example, within endosomes.

Furthermore, the present invention relates to methods for releasing anantigen-binding molecule, which has been bound to an antigen andinternalized into a cell, in an antigen-free form to the outside of thecell, by impairing the antigen-binding ability of the antigen-bindingmolecule at acidic pH as compared that at neutral pH. In the presentinvention, “releasing an antigen-binding molecule, which has been boundto an antigen and internalized into a cell, in an antigen-free form tothe outside of the cell” does not necessarily mean that everyantigen-binding molecule, which has been bound to an antigen andinternalized into a cell, is released in an antigen-free form to theoutside of the cell. It is acceptable that the proportion ofantigen-binding molecules that are released to the outside of the cellincreases when compared to before impairing the antigen-binding abilityof the antigen-binding molecule at acidic pH as compared to that atneutral pH. It is preferred that the antigen-binding molecule releasedto the outside of a cell retains the antigen-binding ability.Furthermore, the method of releasing an antigen-binding molecule, whichhas been bound to an antigen and internalized into a cell, in anantigen-free form to the outside of the cell can also be referred to asa method of conferring to the antigen-binding molecule a property thatthe antigen-binding molecule becomes more easily released to the outsideof the cell in an antigen-free form when the antigen-binding molecule isbound to an antigen and internalized into a cell.

Furthermore, the present invention relates to methods for increasing theability of the antigen-binding molecules to eliminate antigens in plasmaby impairing the antigen-binding ability of the antigen-bindingmolecules at acidic pH as compared to that at neutral pH. In the presentinvention “the ability to eliminate antigens in plasma” refers to theability to eliminate from plasma antigens that are present in plasma,when the antigen-binding molecules are administered in vivo or aresecreted in vivo. Thus, in the present invention, “increasing theability of the antigen-binding molecule to eliminate antigen in plasma”means that the rate of elimination of antigens from plasma when theantigen-binding molecules are administered in vivo is accelerated ascompared to that before lowering the antigen-binding ability of theantigen-binding molecules at acidic pH as compared to that at neutralpH. Whether the ability of the antigen-binding molecule to eliminateantigens in plasma is increased can be determined by, for example,administering soluble antigens and antigen-binding molecules in vivo,and then measuring the concentration of soluble antigens in plasma. Whenthe concentration of soluble antigens in plasma after the administrationof soluble antigens and antigen-binding molecules is reduced by loweringthe antigen-binding ability of the antigen-binding molecule at acidic pHthan that at neutral pH, it can be determined that the ability of theantigen-binding molecule to eliminate antigens in plasma is increased.

The present invention also relates to methods for improving thepharmacokinetics of an antigen-binding molecule by substitutinghistidine or non-natural amino acid for at least one amino acid in theantigen-binding molecule or inserting histidine or non-natural aminoacid into the molecule.

Furthermore, the present invention provides methods for increasing thenumber of times of antigen-binding of an antigen-binding molecule bysubstituting histidine or non-natural amino acid for at least one aminoacid in the antigen-binding molecule or inserting histidine ornon-natural amino acid into the molecule.

In addition, the present invention relates to methods for increasing thenumber of antigens that can be bound by an antigen-binding molecule bysubstituting histidine or non-natural amino acid for at least one aminoacid in the antigen-binding molecule or inserting histidine ornon-natural amino acid into the molecule.

The present invention also provides methods for dissociating an antigenwithin a cell from an extracellularly-bound antigen-binding molecule bysubstituting at least one amino acid in the antigen-binding moleculewith histidine or non-natural amino acid, or inserting histidine ornon-natural amino acid into the molecule.

The present invention also provides methods for releasing anantigen-binding molecule, which has been bound to an antigen andinternalized into a cell, in an antigen-free form to the outside of thecell by substituting at least one amino acid in the antigen-bindingmolecule with histidine or non-natural amino acid, or insertinghistidine or non-natural amino acid into the molecule.

The present invention also provides methods for increasing the abilityof the antigen-binding molecule to eliminate antigens in plasma bysubstituting at least one amino acid in the antigen-binding moleculewith histidine or non-natural amino acid, or inserting histidine ornon-natural amino acid into the molecule.

The site of histidine or non-natural amino acid mutation (substitution,insertion, etc.) is not particularly limited. A histidine or non-naturalamino acid may be substituted or inserted at any site. Preferred sitesof histidine or non-natural amino acid substitution or insertioninclude, for example, sites within a region that has an impact on theantigen-binding ability of the antigen-binding molecule. For example,when the antigen-binding molecule is an antibody, such sites include anantibody variable region or CDR. The number of histidine or non-naturalamino acid mutations is not particularly limited. Histidine ornon-natural amino acid may be substituted or inserted at a single site,or at two or more sites. Furthermore, a deletion, addition, insertion,and/or substitution of other amino acids may be introducedsimultaneously with the histidine or non-natural amino acid substitutionor insertion.

In the present invention, when the antigen-binding molecule is anantibody, possible sites of histidine or non-natural amino acidsubstitution include, for example, sites within the CDR sequence orsequence responsible for the CDR structure of an antibody. Such sitesinclude, for example, the sites listed below. The amino acid positionsare numbered based on the Kabat numbering (Kabat E A et al., (1991)Sequences of Proteins of Immunological Interest, NIH).

-   -   Heavy chain: H27, H31, H32, H33, H35, H50, H58, H59, H61, H62,        H63, H64, H65, H99, H100b, and H102

Light chain: L24, L27, L28, L32, L53, L54, L56, L90, L92, and L94

Among the above sites, H32, H61, L53, L90, and L94 could be universalmodification sites.

When the antigen is the IL-6 receptor (e.g., human IL-6 receptor),preferable modification sites include the following. However, themodification sites are not particularly limited thereto.

Heavy chain: H27, H31, H32, H35, H50, H58, H61, H62, H63, H64, H65,H100b, and H102

Light chain: L24, L27, L28, L32, L53, L56, L90, L92, and L94

When histidine or non-natural amino acid is substituted at multiplesites, preferred combinations of substitution sites include, forexample, the combination of H27, H31, and H35; combination of H27, H31,H32, H35, H58, H62, and H102; combination of L32 and L53; andcombination of L28, L32, and L53. In addition, preferred combinations ofsubstitution sites of heavy and light chains include the combination ofH27, H31, L32, and L53.

When the antigen is IL-6 (e.g., human IL-6), preferable modificationsites include the following. However, the modification sites are notparticularly limited thereto.

Heavy chain: H32, H59, H61, and H99

Light chain: L53, L54, L90, and L94

When the antigen is the IL-31 receptor (e.g., human IL-31 receptor),preferable modification sites include H33. However, the modificationsites are not particularly limited thereto.

Regarding the above sites, only one site may be substituted withhistidine or non-natural amino acid. Alternatively, multiple sites maybe substituted with histidine or non-natural amino acid.

The methods of the present invention are applicable to anyantigen-binding molecules, regardless of the type of target antigen.

The antigen-binding molecules of the present invention are notparticularly limited as long as they have the specific binding activityto an antigen of interest. Preferred antigen-binding molecules of thepresent invention include, for example, substances having anantigen-binding domain of an antibody. The antigen-binding domain of anantibody includes, for example, CDR and variable region. When theantigen-binding domain of an antibody is CDR, the antigen-bindingmolecule may include all of the six CDRs of a whole antibody, or one, ortwo or more of them. Alternatively, when an antigen-binding moleculeincludes CDR as a binding domain of an antibody, the CDR may includeamino acid deletion, substitution, addition, and/or insertion, or may bea partial CDR.

Furthermore, when the antigen-binding molecule includes an antibodyconstant region, the present invention relates to methods for improvingthe pharmacokinetics of antigen-binding molecules by modification (forexample, amino acid substitution, deletion, addition, and/or insertion)of the antibody constant region in the antigen-binding molecule.

In addition, when the antigen-binding molecule includes an antibodyconstant region, the present invention provides methods for increasingthe number of times of antigen-binding of an antigen-binding molecule bymodification (for example, amino acid substitution, deletion, addition,and/or insertion) of the antibody constant region in the antigen-bindingmolecule.

Furthermore, when the antigen-binding molecule includes an antibodyconstant region, the present invention relates to methods for increasingthe number of antigens that can be bound by an antigen-binding moleculeby modification (for example, amino acid substitution, deletion,addition, and/or insertion) of the antibody constant region in theantigen-binding molecule.

Furthermore, when the antigen-binding molecule includes an antibodyconstant region, the present invention relates to methods fordissociating within a cell an antigen from an extracellularly-boundantigen-binding molecule by modification (for example, amino acidsubstitution, deletion, addition, and/or insertion) of the antibodyconstant region in the antigen-binding molecule.

Furthermore, when the antigen-binding molecule includes an antibodyconstant region, the present invention relates to methods for releasingan antigen-binding molecule, which has been bound to an antigen andinternalized into a cell, in an antigen-free form to the outside of thecell, by modification (for example, amino acid substitution, deletion,addition, and/or insertion) of the antibody constant region in theantigen-binding molecule.

Furthermore, when the antigen-binding molecule includes an antibodyconstant region, the present invention relates to methods for increasingthe ability of an antigen-binding molecule to eliminate antigens inplasma by modification (for example, amino acid substitution, deletion,addition, and/or insertion) of the antibody constant region in theantigen-binding molecule.

In a preferred embodiment, the antigen-binding substance of the presentinvention includes antigen-binding substances including an FcRn-bindingregion. After internalized into cells, antigen-binding substancesincluding an FcRn-binding region can return to the plasma by the FcRnsalvage pathway. The FcRn-binding region is preferably a domain thatdirectly binds to FcRn. Preferred FcRn-binding region includes, forexample, antibody Fc regions. However, the FcRn-binding region of thepresent invention may be a region that can bind to a polypeptide havingthe ability to bind to FcRn such as albumin or IgG, since such regionthat can bind to the polypeptide having FcRn-binding ability can bindsindirectly to FcRn via albumin, IgG, etc.

Antigens recognized by antigen-binding molecules such as antibodies ofinterest in the methods of the present invention are not particularlylimited. Such antibodies of interest may recognize any antigen.Antibodies whose pharmacokinetics is to be improved by the methods ofthe present invention include, for example, antibodies that recognizemembrane antigens such as receptor proteins (membrane-bound receptorsand soluble receptors) and cell surface markers, and antibodies thatrecognize soluble antigens such as cytokines. Preferred examples ofmembrane antigens of the present invention include membrane proteins.Examples of soluble antigens of the present invention include solubleproteins. Antigens recognized by antibodies whose pharmacokinetics is tobe improved by the methods of the present invention include, forexample, IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-10,IL-11, IL-12, IL-15, IL-31, IL-23, IL-2 receptor, IL-6 receptor, OSMreceptor, gp130, IL-5 receptor, CD40, CD4, Fas, osteopontin, CRTH2,CD26, PDGF-D, CD20, monocyte chemotactic factor, CD23, TNF-α, HMGB-1, a4integrin, ICAM-1, CCR2, CD11a, CD3, IFNγ, BLyS, HLA-DR, TGF-β, CD52, andIL-31 receptor. Particularly preferred antigens include IL-6 receptor.

Furthermore, the antigen-binding molecule of interest in the methods ofthe present invention includes antigen-binding molecules having anantagonistic activity (antagonistic antigen-binding molecules) andantigen-binding molecules having an agonistic activity (agonisticantigen-binding molecules). In a preferred embodiment, theantigen-binding molecule includes antagonistic antigen-bindingmolecules, in particular, antagonistic antigen-binding molecules thatrecognize membrane antigens such as receptors, or soluble antigens suchas cytokines. For example, an antagonistic antigen-binding molecule thatrecognizes a receptor inhibits the ligand-receptor binding by binding tothe receptor, and thus inhibits the signaling mediated via the receptor.

In the present invention, the antigen-binding molecule of interest isnot particularly limited, and may be any antigen-binding molecules. Theantigen-binding molecule of the present invention preferably includesboth antigen-binding activity (antigen-binding region) and FcRn-bindingregion. In particular, preferred antigen-binding molecule of the presentinvention includes a region that binds to human FcRn. Theantigen-binding molecule including both antigen-binding activity andFcRn-binding region includes, for example, antibodies. The antibodiespreferred in the context of the present invention include, for example,IgG antibodies. When the antibody to be used is an IgG antibody, thetype of IgG is not limited; the IgG belonging to any isotype (subclass)such as IgG1, IgG2, IgG3, or IgG4 can be used. Furthermore, amino acidmutations (e.g., M73) may be introduced into the constant region of anyof these IgG isotypes. Amino acid mutations to be introduced include,for example, those potentiate or impair the binding to Fc□ receptor(Proc Natl Acad Sci USA. 2006 Mar. 14; 103(11):4005-10) and thosepotentiate or impair the binding to FcRn (J Biol Chem. 2001 Mar. 2;276(9):6591-604), but are not limited to these examples. Alternatively,it is also possible to alter the pH-dependent binding by selecting anappropriate constant region such as of IgG2.

When the antigen-binding molecule of interest of the present inventionis an antibody, it may be an antibody derived from any animal, such as amouse antibody, human antibody, rat antibody, rabbit antibody, goatantibody, or camel antibody. Furthermore, the antibody may be a modifiedantibody, for example, a chimeric antibody, and in particular, amodified antibody including amino acid substitution in the sequence of ahumanized antibody, etc. The antibodies also include bispecificantibodies, antibody modification products linked with variousmolecules, and polypeptides including antibody fragments.

“Chimeric antibodies” are antibodies prepared by combining sequencesderived from different animals. Specifically, the chimeric antibodyincludes, for example, antibodies having heavy and light chain variable(V) regions from a mouse antibody and heavy and light chain constant (C)regions from a human antibody.

“Humanized antibodies”, also referred to as reshaped human antibodies,are antibodies in which complementarity determining regions (CDRs) of anantibody derived from a nonhuman mammal, for example, a mouse, aretransplanted into the CDRs of a human antibody. Methods for identifyingCDRs are known (Kabat et al., Sequence of Proteins of ImmunologicalInterest (1987), National Institute of Health, Bethesda, Md.; Chothia etal., Nature (1989) 342:877). General genetic recombination technologiessuitable for this purpose are also known (see European PatentApplication EP 125023; and WO 96/02576).

Bispecific antibody refers to an antibody that has, in the same antibodymolecule, variable regions that recognize different epitopes. Abispecific antibody may be an antibody that recognizes two or moredifferent antigens, or an antibody that recognizes two or more differentepitopes on a same antigen.

Furthermore, polypeptides including antibody fragments include, forexample, Fab fragments, F(ab′)2 fragments, scFv (Nat Biotechnol. 2005September; 23(9):1126-36), domain antibodies (dAb) (WO 2004/058821, WO2003/002609), scFv-Fc (WO 2005/037989), dAb-Fc, and Fc fusion proteins.Of these, molecules including an Fc domain have the activity of bindingto FcRn, and are therefore suitable for use in the methods discovered inthe present invention.

Further, the antigen-binding molecules that are applicable to thepresent invention may be antibody-like molecules. An antibody-likemolecule is a molecule that can exhibit functions by binding to a targetmolecule (Current Opinion in Biotechnology 2006, 17:653-658; CurrentOpinion in Biotechnology 2007, 18:1-10; Current Opinion in StructuralBiology 1997, 7:463-469; Protein Science 2006, 15:14-27), and includes,for example, DARPins (WO 2002/020565), Affibody (WO 1995/001937), Avimer(WO 2004/044011; WO 2005/040229), and Adnectin (WO 2002/032925). Ifthese antibody-like molecules can bind to target molecules in apH-dependent manner, it is possible for a single molecule to bindmultiple target molecules.

Furthermore, the antigen-binding molecule may be a receptor protein or areceptor-Fc fusion protein that binds to a target, including, forexample, TNFR-Fc fusion protein, IL1R-Fc fusion protein, VEGFR-Fc fusionprotein, and CTLA4-Fc fusion protein (Nat Med. 2003 January; 9(1):47-52;BioDrugs. 2006; 20(3):151-60). If such receptor proteins and receptor-Fcfusion proteins can bind to target molecules in a pH-dependent manner,it is possible for a single molecule to bind multiple target molecules.

Moreover, the antigen-binding molecule may be an artificial ligandprotein or artificial ligand fusion protein that binds to a target andhas the neutralizing effect, and includes, for example, mutant IL-6(EMBO J. 1994 Dec. 15; 13(24):5863-70). If such artificial ligandproteins and artificial ligand fusion proteins can bind to targetmolecules in a pH-dependent manner, it is possible for a single moleculeto bind multiple target molecules.

Furthermore, the antibodies of the present invention may includemodified sugar chains. Antibodies with modified sugar chains include,for example, antibodies with modified glycosylation (WO 99/54342),antibodies that are deficient in fucose that is added to the sugar chain(WO 00/61739; WO 02/31140; WO 2006/067847; WO2 006/067913), andantibodies having sugar chains with bisecting GlcNAc (WO 02/79255).

Although the methods of the present invention are not limited to anyspecific theory, the relationship between making the antigen-bindingability at acidic pH weaker as compared to that at neutral pH, theimprovement of the pharmacokinetics, and the multiple-time binding tothe antigen can be explained as follows, for instance.

For example, when the antibody is an antibody that binds to a membraneantigen, the antibody administered into the body binds to the antigenand then is taken up via internalization into endosomes in the cellstogether with the antigen and while the antibody is kept bound to theantigen. Then, the antibody translocates to lysosomes while the antibodyis kept bound to the antigen, and the antibody is degraded by thelysosome together with the antigen. The internalization-mediatedelimination from the plasma is called antigen-dependent elimination, andsuch elimination has been reported with numerous antibody molecules(Drug Discov Today. 2006 January; 11(1-2):81-8). When a single moleculeof IgG antibody binds to antigens in a divalent manner, the singleantibody molecule is internalized while the antibody is kept bound tothe two antigen molecules, and degraded in the lysosome. Accordingly, inthe case of typical antibodies, one molecule of IgG antibody cannot bindto three or more molecules of antigen. For example, a single IgGantibody molecule having a neutralizing activity cannot neutralize threeor more antigen molecules.

The relatively prolonged retention (slow elimination) of IgG moleculesin the plasma is due to the function of FcRn which is known as a salvagereceptor of IgG molecules. When taken up into endosomes via pinocytosis,IgG molecules bind to FcRn expressed in the endosomes under the acidiccondition in the endosomes. While IgG molecules that did not bind toFcRn transfer to lysosomes where they are degraded, IgG molecules thatbound to FcRn translocate to the cell surface and return again in theplasma by dissociating from FcRn under the neutral condition in theplasma.

Alternatively, when the antigen is an antigen that binds to a solubleantigen, the antibody administered into the body binds to the antigenand then is taken up into cells while the antibody is kept bound to theantigen. Many antibodies taken up into cells are released to the outsideof cells via FcRn. However, since the antibodies are released to theoutside of cells, with the antibodies kept bound to antigens, theantibodies cannot bind to antigens again. Thus, similar to antibodiesthat bind to membrane antigens, in the case of typical antibodies, onemolecule of IgG antibody cannot bind to three or more antigen molecules.

The present inventors reasoned that, when antibodies that bound toantigens such as membrane antigens are taken up into endosomes byinternalization, while the antibodies that are kept bound to theantigens translocate to lysosomes and are degraded, the IgG antibodieswhose antigens dissociated in the endosomes could bind to FcRn that areexpressed in the endosomes. Specifically, the present inventorsdiscovered that an antibody that strongly binds to an antigen in theplasma but weakly binds to the antigen within the endosome can bind toan antigen in plasma and be taken up while kept forming a complex withthe antigen into endosomes in the cells via internalization; dissociatefrom the antigen in the endosome; then bind to FcRn and translocate tothe cell surface; and return again in the plasma in a state not bound toantigens to neutralize multiple membrane-bound antigens. Furthermore,the present inventors discovered that an antibody having the property ofstrongly binding to antigens in the plasma but weakly binding toantigens in the endosome can dissociate from the antigens in theendosome even when the antibody had bound to antigens such as solubleantigens; therefore, they are released again into the plasma in a statenot bound to antigens and can neutralize multiple soluble antigens.

In particular, the present inventors noted that the pH in the plasma wasdifferent from the pH in the endosomes, and thus discovered thatantibodies that strongly bind to antigens under plasma pH condition butthat weakly bind to antigens under endosomal pH condition were superiorin retention in the plasma, because one antibody molecule could bind tomultiple antigens.

The endosomes, which are membrane vesicles, form networks in thecytoplasm of eukaryotic cells and are responsible for the metabolism ofmacromolecules in the process from the cell membrane to the lysosomes.The pH in the endosomes has been reported be generally an acidic pH of5.5 to 6.0 (Nat Rev Mol Cell Biol. 2004 February; 5(2):121-32).Meanwhile, the pH in the plasma is known to be almost neutral (normally,pH 7.4).

Accordingly, an antigen-binding molecule whose antigen-binding activityat acidic pH is weaker than the antigen-binding activity at neutral pHbinds to the antigen in the plasma which have a neutral pH, is taken upinto cells, and then dissociates from the antigen in the endosomes whichhave an acidic pH. The antigen-binding molecule that dissociated fromthe antigen binds to FcRn, translocates to the cell surface, and returnsagain in the plasma in a state not bound to antigens. As a result, theantigen-binding molecule can bind to antigens multiple times, and thepharmacokinetics is improved.

<Antigen-Binding Molecule Substances>

Furthermore, the present invention provides antigen-binding moleculeswhose antigen-binding activity at pH 4.0 to pH 6.5 is lower than that atpH 6.7 to pH 10.0, preferably antigen-binding molecules whoseantigen-binding activity at pH 5.0 to pH 6.0 is lower than that at pH7.0 to 8.0. Specifically, antigen-binding molecules whoseantigen-binding activity at pH 4.0 to pH 6.5 is lower than that at pH6.7 to pH 10.0 include, for example, antigen-binding molecules whoseantigen-binding activity at pH 5.8 is lower than that at pH 7.4.Antigen-binding molecules whose antigen-binding activity at pH 5.8 islower than that at pH 7.4 can also be expressed as antigen-bindingmolecules whose antigen-binding activity at pH 7.4 is higher than thatat pH 5.8.

As for the antigen-binding molecules of the present invention whoseantigen-binding activity at pH 5.8 is lower than that at pH 7.4, so longas the antigen-binding activity at pH 5.8 is lower than the binding atpH 7.4, there is no limitation on the difference in binding activity,and the antigen-binding activity at pH 5.8 only need to be lower, evenslightly.

A preferred embodiment of an antigen-binding molecule of the presentinvention whose antigen-binding activity at pH 5.8 is lower than that atpH 7.4 includes antigen-binding molecules whose antigen-binding activityat pH 7.4 is twice or greater than that at pH 5.8. A more preferredembodiment of the antigen-binding molecule includes antigen-bindingmolecules whose antigen-binding activity at pH 7.4 is ten times orgreater than that at pH 5.8. A still more preferred embodiment of theantigen-binding molecule includes antigen-binding molecules whoseantigen-binding activity at pH 7.4 is 40 times or greater than that atpH 5.8.

Specifically, in a preferred embodiment, the antigen-binding molecule ofthe present invention has antigen-binding activity at pH 5.8 that islower than that at pH 7.4, wherein the value of KD(pH5.8)/KD(pH7.4),which is a ratio of KD for the antigen at pH 5.8 and that at pH 7.4, ispreferably 2 or greater, more preferably 10 or greater, and still morepreferably 40 or greater. The upper limit of the KD(pH5.8)/KD(pH7.4)value is not particularly limited, and may be any value, for example,400, 1000, or 10000, as long as production is possible using thetechnologies of those skilled in the art.

In another preferred embodiment, the antigen-binding molecule of thepresent invention whose antigen-binding activity at pH 5.8 is lower thanthat at pH 7.4, has a value of kd(pH5.8)/kd(pH7.4), which is a ratio ofthe kd for the antigen at pH 5.8 and the kd for the antigen at pH 7.4,that is 2 or greater, more preferably 5 or greater, even more preferably10 or greater, and still more preferably 30 or greater. The upper limitof the kd(pH5.8)/kd(pH7.4) value is not particularly limited, and may beany value, for example, 50, 100, or 200, as long as production ispossible using the technologies of those skilled in the art.

Conditions other than the pH at which the antigen-binding activity ismeasured can be appropriately selected by those skilled in the art, andthe conditions are not particularly limited; however, the measurementscan be carried out, for example, under conditions of MES buffer and 37°C., as described in the Examples. Furthermore, the antigen-bindingactivity of an antigen-binding molecule can be determined by methodsknown to those skilled in the art, for example, using a Biacore™ T100surface plasmon resonance system (GE Healthcare) or the like, asdescribed in the Examples.

It is presumed that such an antigen-binding molecule, which weakly bindsto an antigen at acidic pH, easily dissociates from the antigen underthe endosomal acidic condition, and that after internalization intocells, it binds to FcRn and is easily released to the outside of thecells. The antigen-binding molecule released to the outside of the cellswithout being degraded inside the cells can bind again to otherantigens. Accordingly, when the antigen-binding molecule is, forexample, an antigen-binding neutralizing molecule, the antigen-bindingmolecule that easily dissociates from the antigen under the endosomalacidic condition can bind and neutralize antigens multiple times. As aresult, antigen-binding molecules whose antigen-binding activity at pH4.0 to pH 6.5 is lower than that at pH 6.7 to pH 10.0 are superior inretention in the plasma.

In a preferred embodiment, the antigen-binding molecule whoseantigen-binding activity at pH 5.8 is lower than that at pH 7.4 includesantigen-binding molecules in which at least one amino acid in theantigen-binding molecule is substituted with histidine or a non-naturalamino acid, or in which at least one histidine or a non-natural aminoacid has been inserted. The site into which the histidine or non-naturalamino acid mutation is introduced is not particularly limited and may beany site, as long as the antigen-binding activity at pH 5.8 is weakerthan that at pH 7.4 (the KD(pH5.8)/KD(pH7.4) value is greater or thekd(pH5.8)/kd(pH7.4) value is greater) as compared to beforesubstitution. Examples include variable regions and CDRs of an antibodyin the case the antigen-binding molecule is an antibody. The number ofamino acids to be substituted with histidine or non-natural amino acidand the number of amino acids to be inserted can be appropriatelydetermined by those skilled in the art. One amino acid may besubstituted with histidine or non-natural amino acid, or one amino acidmay be inserted, or two or more amino acids may be substituted withhistidine or non-natural amino acids, or two or more amino acids may beinserted. Moreover, apart from the substitutions to histidine or tonon-natural amino acid or insertion of histidine or of non-natural aminoacid, deletion, addition, insertion, and/or substitution and such ofother amino acids may also be simultaneously carried out. Substitutionsto histidine or to non-natural amino acid or insertion of histidine orof non-natural amino acid may be carried out at random using a methodsuch as histidine scanning, which uses histidine instead of alanine inalanine scanning which is known to those skilled in the art.Antigen-binding molecules whose KD(pH5.8)/KD(pH7.4) orkd(pH5.8)/kd(pH7.4) is increased as compared to before mutation can beselected from antigen-binding molecules into which histidine ornon-natural amino acid mutation has been introduced at random.

Preferred antigen-binding molecules with mutation to histidine or tonon-natural amino acid and whose antigen-binding activity at pH 5.8 islower than that at pH 7.4 include, for example, antigen-bindingmolecules whose antigen-binding activity at pH 7.4 after the mutation tohistidine or to non-natural amino acid is equivalent to theantigen-binding activity at pH 7.4 before the mutation to histidine orto non-natural amino acid. In the present invention, “an antigen-bindingmolecule after histidine or non-natural amino acid mutation has anantigen-binding activity that is equivalent to that of theantigen-binding molecule before histidine or non-natural amino acidmutation” means that, when the antigen-binding activity of anantigen-binding molecule before histidine or non-natural amino acidmutation is set as 100%, the antigen-binding activity of theantigen-binding molecule after histidine or non-natural amino acidmutation is at least 10% or more, preferably 50% or more, morepreferably 80% or more, and still more preferably 90% or more. Theantigen-binding activity at pH 7.4 after histidine or non-natural aminoacid mutation may be greater than the antigen-binding activity at pH 7.4before histidine or non-natural amino acid mutation. When theantigen-binding activity of the antigen-binding molecule is decreaseddue to substitution or insertion of histidine or non-natural amino acid,the antigen-binding activity may be adjusted by introducingsubstitution, deletion, addition, and/or insertion and such of one ormore amino acids into the antigen-binding molecule so that theantigen-binding activity becomes equivalent to that before histidinesubstitution or insertion. The present invention also includes suchantigen-binding molecules whose binding activity has been madeequivalent as a result of substitution, deletion, addition, and/orinsertion of one or more amino acids after histidine substitution orinsertion.

Further, when the antigen-binding molecule is a substance including anantibody constant region, in another preferred embodiment of theantigen-binding molecule whose antigen-binding activity at pH 5.8 islower than that at pH 7.4, the present invention includes methods formodifying antibody constant regions contained in the antigen-bindingmolecules. Specific examples of antibody constant regions aftermodification include the constant regions described in the Examples.

When the antigen-binding activity of the antigen-binding substance at pH5.8 is weakened compared to that at pH 7.4 (when KD(pH5.8)/KD(pH7.4)value is increased) by the above described methods and such, it isgenerally preferable that the KD(pH5.8)/KD(pH7.4) value is two times ormore, more preferably five times or more, and even more preferably tentimes or more as compared to that of the original antibody, but is notparticularly limited thereto.

The antigen-binding molecules of the present invention may further haveany other property, as long as their antigen-binding activity at pH 4.0to pH 6.5 is lower than that at pH 6.7 to pH 10.0. For example, theantigen-binding molecules may be agonistic or antagonisticantigen-binding molecules. Preferred antigen-binding molecules of thepresent invention include, for example, antagonistic antigen-bindingmolecules. In general, an antagonistic antigen-binding molecule inhibitsreceptor-mediated intracellular signaling by inhibiting the bindingbetween a ligand (agonist) and the receptor.

Furthermore, the present invention provides antibodies in which aminoacid on at least one site indicated below is substituted with histidineor non-natural amino acid. Amino acid positions are indicated based onthe Kabat numbering (Kabat E A et al., (1991) Sequences of Proteins ofImmunological Interest, NIH).

Heavy chain: H27, H31, H32, H33, H35, H50, H58, H59, H61, H62, H63, H64,H65, H99, H100b, and H102

Light chain: L24, L27, L28, L32, L53, L54, L56, L90, L92, and L94

Among the above sites, H32, H61, L53, L90, and L94 could be universalmodification sites.

When the antigen is the IL-6 receptor (e.g., human IL-6 receptor),preferable modification sites include the following. However, themodification sites are not particularly limited thereto.

Heavy chain: H27, H31, H32, H35, H50, H58, H61, H62, H63, H64, H65,H100b, and H102

Light chain: L24, L27, L28, L32, L53, L56, L90, L92, and L94

When histidine or non-natural amino acid is substituted at multiplesites, preferred combinations of substitution sites include, forexample, the combination of H27, H31, and H35; combination of H27, H31,H32, H35, H58, H62, and H102; combination of L32 and L53; andcombination of L28, L32, and L53. In addition, preferred combinations ofsubstitution sites of heavy and light chains include the combination ofH27, H31, L32, and L53.

When the antigen is IL-6 (e.g., human IL-6), preferable modificationsites include the following. However, the modification sites are notparticularly limited thereto.

Heavy chain: H32, H59, H61, and H99

Light chain: L53, L54, L90, and L94

When the antigen is the IL-31 receptor (e.g., human IL-31 receptor),preferable modification sites include H33. However, the modificationsites are not particularly limited thereto.

The antigen-binding molecules of the present invention may recognize anyantigen. Antigens recognized by antibodies of the present inventionspecifically include the above-mentioned receptor proteins(membrane-bound receptors or soluble receptors), membrane antigens suchas cell surface markers, and soluble antigens such as cytokines, forexample, IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-10,IL-11, IL-12, IL-15, IL-31, IL-23, IL-2 receptor, IL-6 receptor, OSMreceptor, gp130, IL-5 receptor, CD40, CD4, Fas, osteopontin, CRTH2,CD26, PDGF-D, CD20, monocyte chemoattractant factor, CD23, TNF-α,HMGB-1, a4 integrin, ICAM-1, CCR2, CD11a, CD3, IFNγ, BLyS, HLA-DR,TGF-β, CD52, and IL-31 receeptor.

Particularly preferred antigens include the IL-6 receptor.

The antigen-binding molecules of the present invention are describedabove.

In a preferred embodiment of the present invention, the antigen-bindingmolecules include antibodies. Antibodies having antigen-binding activityand FcRn-binding region include, for example, IgG antibodies. When theantibody used is an IgG antibody, there is no limitation as to its type.It is possible to use IgG1, IgG2, IgG3, IgG4, and such.

The origin of antibody of the present invention is not particularlylimited, and may be of any origin. It is possible to use, for example,mouse antibodies, human antibodies, rat antibodies, rabbit antibodies,goat antibodies, camel antibodies, and others. Furthermore, theantibodies may be, for example, the above-described chimeric antibodies,and in particular, modified antibodies with amino acid sequencesubstitutions, such as humanized antibodies. The antibodies may also bethe above-described bispecific antibodies, antibody modificationproducts to which various molecules have been linked, polypeptidesincluding antibody fragments, and antibodies with modified sugar chains.

Generation of chimeric antibodies is known. In the case of a human-mousechimeric antibody, for example, a DNA encoding an antibody V region maybe linked to a DNA encoding a human antibody C region; this can beinserted into an expression vector and introduced into a host to producethe chimeric antibody.

“Humanized antibodies” are also referred to as reshaped humanantibodies, and are antibodies in which the complementarity determiningregion (CDR) of a nonhuman mammal, for example a mouse, is transplantedto the CDR of a human antibody. Methods for identifying CDRs are known(Kabat et al., Sequence of Proteins of Immunological Interest (1987),National Institute of Health, Bethesda, Md.; Chothia et al., Nature(1989) 342:877). General genetic recombination technologies suitable forthis purpose are also known (see European Patent Application EP 125023;and WO 96/02576). Humanized antibodies can be produced by known methods,for example, the CDR of a mouse antibody can be determined, and a DNAencoding an antibody in which the CDR is linked to the framework region(FR) of a human antibody is obtained. Humanized antibodies can then beproduced using a system that uses conventional expression vectors. SuchDNAs can be synthesized by PCR, using as primers severaloligonucleotides prepared to have portions that overlap with the endregions of both the CDR and FR (see the method described in WO98/13388). Human antibody FRs linked via CDRs are selected such that theCDRs form a suitable antigen binding site. If required, amino acids inthe FRs of an antibody variable region may be substituted so that theCDRs of the reshaped human antibody can form a suitable antigen bindingsite (Sato, K. et al., Cancer Res. (1993) 53:10.01-6). Amino acidresidues in the FRs that can be modified include portions that directlybind to an antigen via non-covalent bonds (Amit et al., Science (1986)233: 747-53), portions that influence or have an effect on the CDRstructure (Chothia et al., J. Mol. Biol. (1987) 196: 901-17), andportions involved in VH-VL interactions (EP 239400).

When the antibodies of the present invention are chimeric antibodies orhumanized antibodies, the C regions of these antibodies are preferablyderived from human antibodies. For example, Cγ1, Cγ2, Cγ3, and Cγ4 canbe used for the H chain, while Cκ and Cλ can be used for the L chain.Moreover, if required, amino acid mutations may be introduced into thehuman antibody C region to enhance or lower the binding to Fcγ receptoror FcRn or to improve antibody stability or productivity. A chimericantibody of the present invention preferably includes a variable regionof an antibody derived from a nonhuman mammal and a constant regionderived from a human antibody. Meanwhile, a humanized antibodypreferably includes CDRs of an antibody derived from a nonhuman mammaland FRs and C regions derived from a human antibody. The constantregions derived from human antibodies preferably include an FcRn-bindingregion. Such antibodies include, for example, IgGs (IgG1, IgG2, IgG3,and IgG4). The constant regions used for the humanized antibodies of thepresent invention may be constant regions of antibodies of any isotype.A constant region of human IgG is preferably used, though it is notlimited thereto. The FRs derived from a human antibody, which are usedfor the humanized antibodies, are not particularly limited either, andmay be derived from an antibody of any isotype.

The variable and constant regions of chimeric and humanized antibodiesof the present invention may be modified by deletion, substitution,insertion, and/or addition, and such, so long as the binding specificityof the original antibodies is exhibited.

Since the immunogenicity in the human body is lowered, chimeric andhumanized antibodies using human-derived sequences are thought to beuseful when administered to humans for therapeutic purposes or such.

The antibodies of the present invention may be prepared by any method.For example, antibodies whose antigen-binding activity at pH 5.8 isoriginally greater than or comparable to that at pH 7.4 may beartificially modified through histidine substitution described above orthe like so that their antigen-binding activity at pH 5.8 becomes lowerthan that at pH 7.4. Alternatively, antibodies whose antigen-bindingactivity at pH 5.8 is lower than that at pH 7.4 may be selected byscreening a number of antibodies obtained from an antibody library orhybridomas as described below.

When histidine is substituted for amino acids in an antibody, knownsequences may be used for the H chain or L chain amino acid sequence ofthe antibody before introduction of histidine mutations, or amino acidsequences of antibodies newly obtained by methods known to those skilledin the art can also be used. For example, the antibodies may be obtainedfrom an antibody library, or they may be obtained by cloning genesencoding antibodies from hybridomas producing monoclonal antibodies.

Regarding antibody libraries, many antibody libraries are already known,and methods for producing antibody libraries are also known; therefore,those skilled in the art can appropriately obtain antibody libraries.For example, regarding antibody phage libraries, one can refer to theliterature such as Clackson et al., Nature 1991, 352: 624-8; Marks etal., J. Mol. Biol. 1991, 222: 581-97; Waterhouses et al., Nucleic AcidsRes. 1993, 21: 2265-6; Griffiths et al., EMBO J. 1994, 13: 324.0-60;Vaughan et al., Nature Biotechnology 1996, 14: 309-14; and JapanesePatent Kohyo Publication No. (JP-A) H20-504970 (unexamined Japanesenational phase publication corresponding to a non-Japanese internationalpublication). In addition, it is possible to use known methods, such asmethods using eukaryotic cells as libraries (WO 95/15393) and ribosomedisplay methods. Furthermore, technologies to obtain human antibodies bypanning using human antibody libraries are also known. For example,variable regions of human antibodies can be expressed on the surface ofphages as single chain antibodies (scFvs) using phage display methods,and phages that bind to antigens can be selected. Genetic analysis ofthe selected phages can determine the DNA sequences encoding thevariable regions of human antibodies that bind to the antigens. Once theDNA sequences of scFvs that bind to the antigens is revealed, suitableexpression vectors can be produced based on these sequences to obtainhuman antibodies. These methods are already well known, and one canrefer to WO 92/01047, WO 92/20791, WO 93/06213, WO 93/11236, WO93/19172, WO 95/01438, and WO 95/15388.

As for methods for obtaining genes encoding antibodies from hybridomas,known technologies may be basically used, which involve the use ofdesired antigens or cells expressing the desired antigens as sensitizingantigens, using these to perform immunizations according to conventionalimmunization methods, fusing the resulting immune cells with knownparent cells by conventional cell fusion methods, screening monoclonalantibody producing cells (hybridomas) by conventional screening methods,synthesizing cDNAs of antibody variable regions (V regions) from mRNAsof the obtained hybridomas using reverse transcriptase, and linking themwith DNAs encoding the desired antibody constant regions (C regions).

More specifically, sensitizing antigens to obtain the above-describedantibody genes encoding the H chains and L chains include both completeantigens with immunogenicity and incomplete antigens including haptensand the like with no antigenicity; however they are not limited to theseexamples. For example, it is possible to use whole proteins and partialpeptides of proteins of interest. In addition, it is known thatsubstances comprising polysaccharides, nucleic acids, lipids, and suchcan be antigens. Thus, the antigens of the antibodies of the presentinvention are not particularly limited. The antigens can be prepared bymethods known to those skilled in the art, for example, bybaculovirus-based methods (for example, WO 98/46777) and such.Hybridomas can be produced, for example, by the method of Milstein etal. (G. Kohler and C. Milstein, Methods Enzymol. 1981, 73: 3-46) andsuch. When the immunogenicity of an antigen is low, immunization may beperformed after linking the antigen with a macromolecule havingimmunogenicity, such as albumin. Alternatively, if necessary, antigensmay be converted into soluble antigens by linking them with othermolecules. When transmembrane molecules such as membrane antigens (forexample, receptors) are used as antigens, portions of the extracellularregions of the membrane antigens can be used as a fragment, or cellsexpressing transmembrane molecules on their cell surface may be used asimmunogens.

Antibody-producing cells can be obtained by immunizing animals usingappropriate sensitizing antigens described above. Alternatively,antibody-producing cells can be prepared by in vitro immunization oflymphocytes that can produce antibodies. Various mammals can be used forimmunization; such commonly used animals include rodents, lagomorphas,and primates. Such animals include, for example, rodents such as mice,rats, and hamsters; lagomorphas such as rabbits; and primates includingmonkeys such as cynomolgus monkeys, rhesus monkeys, baboons, andchimpanzees. In addition, transgenic animals carrying human antibodygene repertoires are also known, and human antibodies can be obtained byusing these animals (see WO 96/34096; Mendez et al., Nat. Genet. 1997,15: 146-56). Instead of using such transgenic animals, for example,desired human antibodies having binding activity against antigens can beobtained by in vitro sensitization of human lymphocytes with desiredantigens or cells expressing the desired antigens, and then fusing thesensitized lymphocytes with human myeloma cells such as U266 (seeJapanese Patent Application Kokoku Publication No. (JP-B) H01-59878(examined, approved Japanese patent application published foropposition)). Furthermore, desired human antibodies can be obtained byimmunizing transgenic animals carrying a complete repertoire of humanantibody genes, with desired antigens (see WO 93/12227, WO 92/03918, WO94/02602, WO 96/34096, and WO 96/33735).

Animal immunization can be carried out by appropriately diluting andsuspending a sensitizing antigen in phosphate buffered saline (PBS),physiological saline, or such, and mixing it with an adjuvant toemulsify, if necessary. This is then intraperitoneally or subcutaneouslyinjected into animals. Then, the sensitizing antigen mixed with Freund'sincomplete adjuvant is preferably administered several times every fourto 21 days. Antibody production can be confirmed by measuring the titerof the antibody of interest in animal sera using conventional methods.

Antibody-producing cells obtained from lymphocytes or animals immunizedwith a desired antigen can be fused with myeloma cells to generatehybridomas using conventional fusing agents (for example, polyethyleneglycol) (Goding, Monoclonal Antibodies: Principles and Practice,Academic Press, 1986, 59-103). When required, hybridoma cells can becultured and grown, and the binding specificity of the antibody producedfrom these hybridomas can be measured using known analysis methods, suchas immunoprecipitation, radioimmunoassay (MA), and enzyme-linkedimmunosorbent assay (ELISA). Thereafter, hybridomas producing antibodiesof interest whose specificity, affinity, or activity has been determinedcan be subcloned by methods such as limiting dilution.

Next, genes encoding the selected antibodies can be cloned fromhybridomas or antibody-producing cells (sensitized lymphocytes, andsuch) using probes that can specifically bind to the antibodies (forexample, oligonucleotides complementary to sequences encoding theantibody constant regions). It is also possible to clone the genes frommRNA using RT-PCR. Immunoglobulins are classified into five differentclasses, IgA, IgD, IgE, IgG, and IgM. These classes are further dividedinto several subclasses (isotypes) (for example, IgG-1, IgG-2, IgG-3,and IgG-4; IgA-1 and IgA-2; and such). H chains and L chains used in thepresent invention to produce antibodies are not particularly limited andmay originate from antibodies belonging to any of these classes orsubclasses; however, IgG is particularly preferred.

Herein, it is possible to modify H-chain-encoding genes andL-chain-encoding genes using genetic engineering technologies.Genetically modified antibodies, such as chimeric antibodies andhumanized antibodies, which have been artificially modified for thepurpose of decreasing heterologous immunogenicity and such againsthumans, can be appropriately produced for antibodies such as mouseantibodies, rat antibodies, rabbit antibodies, hamster antibodies, sheepantibodies, and camel antibodies. Chimeric antibodies are antibodiesincluding H chain and L chain variable regions of nonhuman mammalantibody, such as mouse antibody, and the H chain and L chain constantregions of human antibody. Chimeric antibodies can be obtained byligating a DNA encoding a variable region of a mouse antibody to a DNAencoding a constant region of a human antibody, inserting this into anexpression vector, and introducing the vector into a host to produce theantibody. A humanized antibody, which is also called a reshaped humanantibody, can be synthesized by PCR using several oligonucleotidesproduced so that they have overlapping portions at the ends of DNAsequences designed to link the complementarity determining regions(CDRs) of an antibody of a nonhuman mammal such as a mouse. Theresulting DNA can be ligated to a DNA encoding a human antibody constantregion. The ligated DNA can be inserted into an expression vector, andthe vector can be introduced into a host to produce the antibody (see EP239400 and WO 96/02576). Human antibody FRs that are ligated via the CDRare selected when the CDR forms a favorable antigen-binding site. Ifnecessary, amino acids in the framework region of an antibody variableregion may be substituted such that the CDR of the reshaped humanantibody forms an appropriate antigen-binding site (K. Sato et al.,Cancer Res. 1993, 53: 10.01-10.06).

In addition to the humanization described above, antibodies may bemodified to improve their biological properties, for example, thebinding to the antigen. In the present invention, such modifications canbe achieved by methods such as site-directed mutagenesis (see forexample, Kunkel (1910.0) Proc. Natl. Acad. Sci. USA 82: 488), PCRmutagenesis, and cassette mutagenesis. In general, mutant antibodieswhose biological properties have been improved show amino acid sequencehomology and/or similarity of 70% or higher, more preferably 80% orhigher, and even more preferably 90% or higher (for example, 95% orhigher, 97%, 98%, or 99%), when compared to the amino acid sequence ofthe original antibody variable region. Herein, sequence homology and/orsimilarity is defined as the ratio of amino acid residues that arehomologous (same residue) or similar (amino acid residues classifiedinto the same group based on the general properties of amino acid sidechains) to the original antibody residues, after the sequence homologyvalue has been maximized by sequence alignment and gap introduction, ifnecessary. In general, natural amino acid residues are classified intogroups based on the characteristics of their side chains as follows:

-   -   (1) hydrophobic: alanine, isoleucine, valine, methionine, and        leucine;    -   (2) neutral hydrophilic: asparagine, glutamine, cysteine,        threonine, and serine;    -   (3) acidic: aspartic acid and glutamic acid;    -   (4) basic: arginine, histidine, and lysine;    -   (5) residues that affect the orientation of the chain: glycine,        and proline; and    -   (6) aromatic: tyrosine, tryptophan, and phenylalanine.

In general, a total of six complementarity determining regions (CDRs;hypervariable regions) present on the H chain and L chain variableregions interact with each other to form an antigen-binding site of anantibody. A variable region alone is also known to be capable ofrecognizing and binding to an antigen, although its affinity is lowerthan the affinity of the whole binding site. Thus, antibody genesencoding the H chain and L chain of the present invention may encodefragments each including the H chain or L chain antigen-binding site, aslong as the polypeptide encoded by the gene retains the activity ofbinding to the desired antigen.

As described above, the heavy chain variable region is in generalconstituted by three CDRs and four FRs. In a preferred embodiment of thepresent invention, amino acid residues to be “modified” can beappropriately selected from amino acid residues, for example, in a CDRor FR. In general, modifications of amino acid residues in the CDRs mayreduce the antigen-binding ability. Thus, appropriate amino acidresidues to be “modified” in the present invention are preferablyselected from amino acid residues in the FRs, but are not limitedthereto. It is possible to select amino acids in a CDR as long as themodification has been confirmed not to reduce the binding ability.Alternatively, by using public databases or such, those skilled in theart can obtain appropriate sequences that can be used as an FR ofantibody variable region of an organism such as human or mouse.

Furthermore, the present invention provides genes encoding theantibodies of the present invention. The genes encoding the antibodiesof the present invention may be any genes, and may be DNAs, RNAs,nucleic acid analogs, or the like.

Furthermore, the present invention also provides host cells carrying thegenes described above. The host cells are not particularly limited andinclude, for example, E. coli and various animal cells. The host cellsmay be used, for example, as a production system to produce and expressthe antibodies of the present invention. In vitro and in vivo productionsystems are available for polypeptide production systems. Such in vitroproduction systems include, for example, production systems usingeukaryotic cells or prokaryotic cells.

Eukaryotic cells that can be used as host cells include, for example,animal cells, plant cells, and fungal cells. Animal cells include:mammalian cells, for example, CHO (J. Exp. Med. (1995) 108: 94.0), COS,HEK293, 3T3, myeloma, BHK (baby hamster kidney), HeLa, and Vero;amphibian cells such as Xenopus laevis oocytes (Valle et al., Nature(1981) 291: 338-340); and insect cells such as Sf9, Sf21, and Tn5.CHO-DG44, CHO-DX11B, COS7 cells, HEK293 cells, and BHK cells arepreferably used to express the antibodies of the present invention.Among animal cells, CHO cells are particularly preferable forlarge-scale expression. Vectors can be introduced into host cells, forexample, by calcium phosphate methods, DEAE-dextran methods, methodsusing cationic liposome DOTAP (Boehringer-Mannheim), electroporationmethods, and lipofection methods.

Regarding plant cells, for example, Nicotiana tabacum-derived cells andduckweed (Lemna minor) are known as a protein production system.Calluses can be cultured from these cells to produce the antibodies ofthe present invention. Regarding fungal cells, known protein expressionsystems are those using yeast cells, for example, cells of genusSaccharomyces (such as Saccharomyces cerevisiae and Saccharomycespombe); and cells of filamentous fungi, for example, genus Aspergillus(such as Aspergillus niger). These cells can be used as a host toproduce the antibodies of the present invention.

Bacterial cells can be used in the prokaryotic production systems.Regarding bacterial cells, production systems using Bacillus subtilisare known in addition to the production systems using E. coli describedabove. Such systems can be used in producing the antibodies of thepresent invention.

<Screening Methods>

The present invention provides methods of screening for antigen-bindingmolecules whose antigen-binding activity at acidic pH is lower than thatat neutral pH. The present invention also provides methods of screeningfor antigen-binding molecules which can individually bind to multipleantigens. The present invention also provides methods of screening forantigen-binding molecules which are superior in the retention in plasma.The present invention also provides methods of screening for anantigen-binding molecule that dissociates within a cell from anextracellularly-bound antigen. The present invention also providesmethods of screening for an antigen-binding molecule that is bound to anantigen and internalized into a cell, and released to the outside of thecell in an antigen-free form. The present invention also providesmethods of screening for an antigen-binding molecule that has increasedability to eliminate antigens in plasma. Furthermore, the presentinvention also provides methods of screening for antigen-bindingmolecules which are particularly useful when used as pharmaceuticalcompositions.

Specifically, the present invention provides methods of screening forantigen-binding molecules, which comprise the steps of:

-   -   (a) determining the antigen-binding activity of an        antigen-binding molecule at pH 6.7 to pH 10.0;    -   (b) determining the antigen-binding activity of the        antigen-binding molecule at pH 4.0 to pH 6.5; and    -   (c) selecting an antigen-binding molecule whose antigen-binding        activity at pH 6.7 to pH 10.0 is greater than the        antigen-binding activity at pH 4.0 to pH 6.5.

In the screening methods of the present invention, the antigen-bindingactivity of the antigen-binding molecule at pH 6.7 to pH 10.0 is notparticularly limited, as long as it is an antigen-binding activity at apH between pH 6.7 and pH 10.0. However, for example, a preferredantigen-binding activity is an antigen-binding activity at a pH betweenpH 7.0 and pH 8.0, and a more preferred antigen-binding activity is anantigen-binding activity at pH 7.4. Further, the antigen-bindingactivity of the antigen-binding molecule at pH 4.0 to pH 6.5 is notparticularly limited, as long as it is an antigen-binding activity at apH between pH 4.0 and pH 6.5. However, for example, a preferredantigen-binding activity is an antigen-binding activity at a pH betweenpH 5.5 to pH 6.5, and a more preferred antigen-binding activity is anantigen-binding activity at pH 5.8 or pH 5.5.

The antigen-binding activity of an antigen-binding molecule can bedetermined by methods known to those skilled in the art. Conditionsother than the pH can be appropriately determined by those skilled inthe art. The antigen-binding activity of an antigen-binding molecule canbe assessed as dissociation constant (KD), apparent dissociationconstant (apparent KD), dissociation rate (k_(d)), apparent dissociationrate (apparent k_(d)), or such. These constants can be determined bymethods known to those skilled in the art, for example, using a Biacore™surface plasmon resonance system (GE Healthcare), Scatchard plot, orFACS.

Herein, “the step of selecting an antigen-binding molecule whoseantigen-binding activity at pH 6.7 to pH 10.0 is greater than that at pH4.0 to pH 6.5” has a same meaning as “the step of selecting anantigen-binding molecule whose antigen-binding activity at pH 4.0 to pH6.5 is lower than that at pH 6.7 to pH 10.0”.

The difference between the antigen-binding activity at pH 6.7 to pH 10.0and that at pH 4.0 to pH 6.5 is not particularly limited as long as theantigen-binding activity at pH 6.7 to pH 10.0 is greater than that at pH4.0 to pH 6.5. However, the antigen-binding activity at pH 6.7 to pH10.0 is preferably twice or greater, more preferably ten times orgreater, and still more preferably 40 times or greater than theantigen-binding activity at pH 4.0 to pH 6.5.

Furthermore, the present invention also provides methods of screeningfor antigen-binding molecules, which comprise the steps of:

-   -   (a) binding an antigen-binding molecule to an antigen under a        condition of pH 6.7 to pH 10.0;    -   (b) placing the antigen-binding molecule that bound to the        antigen of (a) under a condition of pH 4.0 to pH 6.5; and    -   (c) obtaining the antigen-binding molecule that dissociated        under the condition of pH 4.0 to pH 6.5.

In addition, the present invention also provides methods of screeningfor antigen-binding molecules, which comprise the steps of:

-   -   (a) selecting an antigen-binding molecule that does not bind to        an antigen under a condition of pH 4.0 to pH 6.5;    -   (b) binding the antigen-binding molecule selected in (a) to an        antigen under a condition of pH 6.7 to pH 10.0; and    -   (c) obtaining the antigen-binding molecule that bound to the        antigen under the condition of pH 6.7 to pH 10.0.

Furthermore, the present invention also provides methods of screeningfor antigen-binding molecules, which comprise the steps of:

-   -   (a) binding an antigen-binding molecule to an antigen under a        condition of pH 6.7 to pH 10.0;    -   (b) placing the antigen-binding molecule that bound to the        antigen of (a) under a condition of pH 4.0 to pH 6.5;    -   (c) obtaining the antigen-binding molecule that dissociated        under the condition of pH 4.0 to pH 6.5;    -   (d) amplifying the gene encoding the antigen-binding molecule        that dissociated; and    -   (e) obtaining the eluted antigen-binding molecule.

The steps of (a) to (d) may be repeated twice or more times. Thus, thepresent invention provides the methods described above further includinga step of repeating the steps of (a) to (d) twice or more times. Thenumber for repeating the steps of (a) to (d) is not particularlylimited; however, the number is in general ten or less.

Furthermore, the present invention also provides methods of screeningfor antigen-binding molecules, which comprise the steps of:

-   -   (a) selecting an antigen-binding molecule that does not bind to        an antigen under a condition of pH 4.0 to pH 6.5;    -   (b) binding the antigen-binding molecule selected in (a) to an        antigen under a condition of pH 6.7 to pH 10.0;    -   (c) obtaining the antigen-binding molecule that bound to the        antigen under the condition of pH 6.7 to pH 10.0;    -   (d) amplifying the gene encoding the antigen-binding molecule        that dissociated; and    -   (e) collecting the eluted antigen-binding molecule.

The steps of (a) to (d) may be repeated twice or more times. Thus, thepresent invention provides the methods described above further includinga step of repeating the steps of (a) to (d) twice or more times. Thenumber for repeating the steps of (a) to (d) is not particularlylimited; however, the number is in general ten or less.

When a phage library or such is used in the screening methods of thepresent invention, the step of amplifying the gene encoding theantigen-binding molecule can also be a step of amplifying phages.

In the methods of the present invention, binding of the antigen-bindingmolecule and the antigen may be carried out under any state, withoutparticular limitation. For example, binding of the antigen-bindingmolecule and the antigen may be carried out by contacting an antigenwith an immobilized antigen-binding molecule, or by contacting anantigen-binding molecule with an immobilized antigen. Alternatively,binding of the antigen-binding molecule and the antigen may be carriedout by contacting the antigen and antigen-binding molecule in asolution.

Furthermore, the present invention also provides methods of screeningfor antigen-binding molecules whose binding activity at a first pH isgreater than that at a second pH, which comprise the steps of:

-   -   (a) binding an antigen-binding molecule to an        antigen-immobilized column under the condition of a first pH;    -   (b) eluting the antigen-binding molecule that had bound to the        column at the first pH from the column under the condition of a        second pH; and    -   (c) obtaining the eluted antigen-binding molecule.

Furthermore, the present invention also provides methods of screeningfor antigen-binding molecules whose binding activity at a first pH issmaller than that at a second pH, which comprise the steps of:

-   -   (a) passing an antigen-binding molecule through an        antigen-immobilized column under the condition of a first pH;    -   (b) collecting the antigen-binding molecule that eluted without        binding to the column in step (a);    -   (c) binding the antigen-binding molecule collected in (b) to a        column under the condition of a second pH; and    -   (d) obtaining the antigen-binding molecule that bound to the        column in step (c).

Furthermore, the present invention also provides methods of screeningfor antigen-binding molecules whose binding activity at a first pH isgreater than that at a second pH, which comprise the steps of:

-   -   (a) binding an antigen-binding molecule library to an        antigen-immobilized column under the condition of a first pH;    -   (b) eluting the antigen-binding molecule from the column under        the condition of a second pH;    -   (c) amplifying the gene encoding the eluted antigen-binding        molecule; and    -   (d) obtaining the eluted antigen-binding molecule.

The steps of (a) to (c) may be repeated twice or more times. Thus, thepresent invention provides the methods described above further includingthe step of repeating the steps of (a) to (c) twice or more times. Thenumber for repeating the steps of (a) to (c) is not particularlylimited; however, the number is in general ten or less.

In the present invention, each of the first and second pHs may be anypH, as long as they are not identical. In a preferred combination of thefirst and second pHs, for example, the first pH is between pH 6.7 and pH10.0, and the second pH is between pH 4.0 and pH 6.5; in a morepreferred combination, the first pH is between pH 7.0 and pH 8.0, andthe second pH is between pH 5.5 and pH 6.5; and in a still morepreferred combination, the first pH is pH 7.4 and the second pH is pH5.8 or pH5.5.

In another preferred combination of the first and second pHs, forexample, the first pH is between pH 4.0 and pH 6.5, and the second pH isbetween pH 6.7 and pH 10.0; in a more preferred combination, the firstpH is between pH 5.5 and pH 6.5, and the second pH is between pH 7.0 andpH 8.0; and in a still more preferred combination, the first pH is pH5.8 or pH5.5 and the second pH is pH 7.4.

Antigen-binding molecules that are screened by the methods of thepresent invention may be any antigen-binding molecules. For example, itis possible to use the above-described antigen-binding molecules in thescreening of the present invention. For example, it is possible toscreen antigen-binding molecules including natural sequences orantigen-binding molecules including amino acid sequences withsubstitutions. Preferred antigen-binding molecules that are screened inthe present invention include, for example, antigen-binding molecules inwhich at least one amino acid is substituted with histidine or at leastone histidine is inserted. The site of introduction of histidinesubstitution or insertion is not particularly limited, and may beintroduced at any site. Furthermore, histidine substitution or insertionmay be introduced at one site, or may be introduced at two or moresites. Furthermore, preferred antigen-binding molecules that arescreened in the present invention include, for example, antigen-bindingmolecules including modified antibody constant regions.

Antigen-binding molecules that are screened by the methods of thepresent invention may be a number of different antigen-binding moleculesintroduced with histidine substitutions or insertions at differentsites, for example, by histidine scanning.

Thus, the screening methods of the present invention may furthercomprise the step of substituting at least one amino acid in theantigen-binding molecule with histidine or inserting at least onehistidine into the antigen-binding molecule.

In the screening methods of the present invention, non-natural aminoacids may be used instead of histidine. Therefore, the present inventioncan also be understood by replacing the above-mentioned histidine withnon-natural amino acids.

Moreover, the screening methods of the present invention may furthercomprise the step of modifying amino acids of antibody constant regions.

Antigen-binding substances that are screened by the screening methods ofthe present invention may be prepared by any method. For example, it ispossible to use pre-existing antibodies, pre-existing libraries (phagelibraries and the like), antibodies and libraries that are prepared fromhybridomas obtained by immunizing animals or from B cells of immunizedanimals, antibodies and libraries (libraries with high content ofhistidine or non-natural amino acid, libraries introduced with histidineor non-natural amino acid at specific sites, and the like) prepared byintroducing histidine mutations or non-natural amino acid mutations intothe above-described antibodies and libraries, and so on.

Antigen-binding molecules that bind to the antigen multiple times, whichare thus superior in the retention in plasma, can be obtained by thescreening methods of the present invention. Thus, the screening methodsof the present invention can be used as screening methods for obtainingantigen-binding molecules that are superior in the retention in plasma.

Furthermore, antigen-binding molecules that can bind to the antigen twoor more times when administered to animals such as humans, mice, ormonkeys can be obtained by the screening methods of the presentinvention. Thus, the screening methods of the present invention can beused as screening methods for obtaining antigen-binding molecules thatcan bind to the antigen two or more times.

Furthermore, antigen-binding molecules that are capable of binding tomore antigens as compared to the number of their antigen-binding siteswhen administered to animals such as humans, mice, or monkeys can beobtained by the screening methods of the present invention. Thus, thescreening methods of the present invention can be used as screeningmethods for obtaining antigen-binding molecules that are capable ofbinding to more antigens as compared to the number of theirantigen-binding sites. For example, when the antibody is a neutralizingantibody, the screening methods of the present invention can be used asscreening methods for obtaining antigen-binding molecules that canneutralize more antigens as compared to the number of theantigen-binding sites of the antigen-binding molecules.

Furthermore, antigen-binding molecules that are capable of dissociatingwithin a cell from an extracellularly-bound antigen when administered toanimals such as humans, mice, or monkeys can be obtained by thescreening methods of the present invention. Thus, the screening methodsof the present invention can be used as screening methods for obtainingantigen-binding molecules that are capable of dissociating within a cellfrom an extracellularly-bound antigen.

Furthermore, antigen-binding molecules that are bound to an antigen andinternalized into a cell, and released to the outside of the cell in anantigen-free form when administered to animals such as humans, mice, ormonkeys can be obtained by the screening methods of the presentinvention. Thus, the screening methods of the present invention can beused as screening methods for obtaining antigen-binding molecules thatare bound to an antigen and internalized into a cell, and released tothe outside of the cell in an antigen-free form.

Furthermore, antigen-binding molecules that can rapidly eliminateantigens in plasma when administered to animals such as humans, mice, ormonkeys can be obtained by the screening methods of the presentinvention. Thus, the screening methods of the present invention can beused as screening methods for obtaining antigen-binding molecules withincreased (high) ability to eliminate antigens in plasma.

Furthermore, such antigen-binding molecules are expected to beespecially superior as pharmaceuticals, because the dose and frequencyof administration in patients can be reduced and as a result the totaldosage can be reduced. Thus, the screening methods of the presentinvention can be used as methods of screening for antigen-bindingmolecules for use as pharmaceutical compositions.

In addition, the present invention provides libraries in which thehistidine content is increased as compared to the original libraries.Libraries containing antigen-binding molecules with increased histidinecontent can be used in the screening methods described above and theproduction methods described hereinafter.

Libraries with increased histidine content can be prepared by methodsknown to those skilled in the art, which include the following method.20 types of triplet codons (trinucleotides) encoding 20 types of aminoacids can be incorporated at equal frequency when synthesizing nucleicacids to prepare a library by the trinucleotide-method (J Mol Biol. 2008Feb. 29; 376(4): 1182-200). As a result, the position mutated for thelibrary can be made to contain 20 types of amino acids at equalprobability. The frequency of histidine in the position mutated for thelibrary can be increased by increasing the proportion of ahistidine-encoding trinucleotide as compared to the remaining aminoacids among the 20 types in the synthesis.

<Methods for Producing Antigen-Binding Molecules>

The present invention provides methods for producing antigen-bindingmolecules whose antigen-binding activity at the endosomal pH is lowerthan that at the plasma pH. The present invention also provides methodsfor producing antigen-binding molecules that are superior in theretention in plasma. The present invention also provides methods forproducing antigen-binding molecules that are especially useful when usedas pharmaceutical compositions.

Specifically, the present invention provides methods for producingantigen-binding molecules, which comprise the steps of:

-   -   (a) determining the antigen-binding activity of an        antigen-binding molecule at pH 6.7 to pH 10.0;    -   (b) determining the antigen-binding activity of the        antigen-binding molecule at pH 4.0 to pH 6.5;    -   (c) selecting an antigen-binding molecule whose antigen-binding        activity at pH 6.7 to pH 10.0 is greater than that at pH 4.0 to        pH 6.5;    -   (d) obtaining the gene encoding the antigen-binding molecule        selected in (c); and    -   (e) producing the antigen-binding molecule using the gene        obtained in (d).

The present invention also provides methods for producingantigen-binding molecules, which comprise the steps of:

-   -   (a) binding an antigen-binding molecule to an antigen at pH 6.7        to pH 10.0;    -   (b) allowing the antigen-binding molecule bound to the antigen        of (a) to stand under the condition of pH 4.0 to pH 6.5;    -   (c) collecting the antigen-binding molecule that dissociated        under the condition of pH 4.0 to pH 6.5;    -   (d) obtaining the gene encoding the antigen-binding molecule        obtained in (c); and    -   (e) producing the antigen-binding molecule using the gene        obtained in (d).

Furthermore, the present invention provides methods for producingantigen-binding molecules, which comprise the steps of:

-   -   (a) selecting an antigen-binding molecule that does not bind to        the antigen under the condition of pH 4.0 to pH 6.5;    -   (b) binding the antigen under the condition of pH 6.7 to pH 10.0        to the antigen-binding molecule selected in (a);    -   (c) collecting the antigen-binding molecule that bound to the        antigen under the condition of pH 6.7 to pH 10.0;    -   (d) obtaining the gene encoding the antigen-binding molecule        collected in (c); and    -   (e) producing the antigen-binding molecule using the gene        obtained in (d).

In addition, the present invention provides methods for producingantigen-binding molecules, which comprise the steps of:

-   -   (a) binding an antigen-binding molecule to an antigen under the        condition of pH 6.7 to 10.0;    -   (b) allowing the antigen-binding molecule that bound to the        antigen in (a) to stand under the condition of pH 4.0 to pH 6.5;    -   (c) collecting the antigen-binding molecule that dissociated        under the condition of pH 4.0 to pH 6.5;    -   (d) amplifying the gene encoding the dissociated antigen-binding        molecule;    -   (e) collecting the eluted antigen-binding molecule;    -   (f) obtaining the gene encoding the antigen-binding molecule        collected in (e); and    -   (g) producing the antigen-binding molecule using the gene        obtained in (f).

Steps (a) to (d) may be repeated twice or more times. Thus, the presentinvention provides the methods described above, which further comprisethe step of repeating steps (a) to (d) twice or more times. The numberof times steps (a) to (d) is repeated is not particularly limited;however, it is generally ten times or less.

Furthermore, the present invention provides methods of screening forantigen-binding molecules, which comprise the steps of:

-   -   (a) selecting an antigen-binding molecule that does not bind to        the antigen under the condition of pH 4.0 to pH 6.5;    -   (b) binding the antigen under the condition of pH 6.7 to pH 10.0        to the antigen-binding molecule selected in (a);    -   (c) collecting the antigen-binding molecule that bound to the        antigen under the condition of pH 6.7 to pH 10.0;    -   (d) amplifying the gene encoding the dissociated antigen-binding        molecule;    -   (e) collecting the eluted antigen-binding molecule;    -   (f) obtaining the gene encoding the antigen-binding molecule        collected in (e); and    -   (g) producing the antigen-binding molecule using the gene        obtained in (f).

Steps (a) to (d) may be repeated twice or more times. Thus, the presentinvention provides the methods described above, which further comprisethe step of repeating steps (a) to (d) twice or more times. The numberof times steps (a) to (d) is repeated is not particularly limited;however, it is generally ten times or less.

Furthermore, the present invention provides methods for producingantigen-binding molecules whose binding activity at a first pH isgreater than that at a second pH, which comprise the steps of:

-   -   (a) binding the antigen-binding molecule to a column immobilized        with antigen under the first pH condition;    -   (b) eluting the antigen-binding molecule, which is bound to the        column under the first pH condition from the column under a        second pH condition;    -   (c) collecting the eluted antigen-binding molecule;    -   (d) obtaining the gene encoding the antigen-binding molecule        collected in (c); and    -   (e) producing the antigen-binding molecule using the gene        obtained in (d).

Furthermore, the present invention provides methods for producingantigen-binding molecules whose binding activity at a first pH isgreater than that at a second pH, which comprise the steps of:

-   -   (a) binding an antigen-binding molecule library to a column        immobilized with antigen under the first pH condition;    -   (b) eluting the antigen-binding molecule from the column under        the second pH condition;    -   (c) amplifying the gene encoding the eluted antigen-binding        molecule;    -   (d) collecting the eluted antigen-binding molecule;    -   (e) obtaining the gene encoding the antigen-binding molecule        collected in (d); and    -   (f) producing the antigen-binding molecule using the gene        obtained in (e).

Steps (a) to (c) may be repeated twice or more times. Thus, the presentinvention provides the methods described above, which further comprisethe step of repeating steps (a) to (c) twice or more times. The numberof times steps (a) to (c) is repeated is not particularly limited;however, it is generally ten times or less.

When a phage library or such is used in the production methods of thepresent invention, the step of amplifying the gene encoding theantigen-binding molecule may be the step of amplifying phages.

Antigen-binding substances that are used in the production methods ofthe present invention may be prepared by any method. For example, it ispossible to use pre-existing antibodies, pre-existing libraries (phagelibraries and the like), antibodies and libraries that are prepared fromhybridomas obtained by immunizing animals or from B cells of immunizedanimals, antibodies and libraries (libraries with high content ofhistidine or non-natural amino acid, libraries introduced with histidineor non-natural amino acid at specific sites, and the like) prepared byintroducing histidine mutations or non-natural amino acid mutations intothe above-described antibodies and libraries, and so on.

In the above-described production methods, the antigen-binding activityof the antigen-binding molecule at pH 6.7 to pH 10.0 is not particularlylimited, as long as the antigen-binding activity is that at a pH betweenpH 6.7 and pH 10.0. A preferred antigen-binding activity is that at a pHbetween pH 7.0 and pH 8.0, and a more preferred antigen-binding activityis that at pH 7.4. Alternatively, the antigen-binding activity of theantigen-binding molecule at pH 4.0 to pH 6.5 is not particularlylimited, as long as the antigen-binding activity is that at a pH betweenpH 4.0 and pH 6.5. A preferred antigen-binding activity is that at a pHbetween pH 5.5 to pH 6.5, and a more preferred antigen-binding activityis that at pH 5.8 or pH 5.5.

The antigen-binding activity of an antigen-binding molecule can bedetermined by methods known to those skilled in the art. Conditionsexcept for pH can be appropriately determined by those skilled in theart.

The step of selecting antigen-binding molecules whose antigen-bindingactivity at pH 6.7 to pH 10.0 is greater than that at pH 4.0 to pH 6.5is synonymous with the step of selecting antigen-binding molecules whoseantigen-binding activity at pH 4.0 to pH 6.5 is lower than that at pH6.7 to pH 10.0.

The difference in the antigen-binding activity at pH 6.7 to pH 10.0 andat pH 4.0 to pH 6.5 is not particularly limited as long as theantigen-binding activity at pH 6.7 to pH 10.0 is greater than that at pH4.0 to pH 6.5. The antigen-binding activity at pH 6.7 to pH 10.0 ispreferably twice or greater, more preferably ten times or greater, andstill more preferably 40 times or greater than that at pH 4.0 to pH 6.5.

In the production methods described above, the antigen-binding moleculemay be bound to the antigen under any condition, and the condition isnot particularly limited. For example, the antigen-binding molecule maybe bound to the antigen by contacting the antigen with the immobilizedantigen-binding molecule, or by contacting the antigen-binding moleculewith the immobilized antigen. Alternatively, the antigen-bindingmolecule may be bound to the antigen by contacting the antigen andantigen-binding molecule in a solution.

In the production methods described above, each of the first and secondpHs may be any pH, as long as they are not identical. In a preferredcombination of the first and second pHs, for example, the first pH isbetween pH 6.7 and pH 10.0, and the second pH is between pH 4.0 and pH6.5; in a more preferred combination, the first pH is between pH 7.0 andpH 8.0, and the second pH is between pH 5.5 and pH 6.5; and in a stillmore preferred combination, the first pH is pH 7.4 and the second pH ispH 5.8 or pH 5.5.

In another preferred combination of the first and second pHs, forexample, the first pH is between pH 4.0 and pH 6.5, and the second pH isbetween pH 6.7 and pH 10.0; in a more preferred combination, the firstpH is between pH 5.5 and pH 6.5, and the second pH is between pH 7.0 andpH 8.0; and in a still more preferred combination, the first pH is pH5.8 or pH 5.5 and the second pH is pH 7.4.

Antigen-binding molecules that are produced by the production methodsdescribed above may be any antigen-binding molecules. Preferredantigen-binding molecules include, for example, antigen-bindingmolecules in which at least one amino acid is substituted with histidineor at least one histidine has been inserted. The site where suchhistidine mutation is introduced is not particularly limited and may beintroduced at any site. Furthermore, histidine mutation may beintroduced at one site or at two or more sites.

Thus, the production methods of the present invention may furthercomprise the step of substituting at least one amino acid in anantigen-binding molecule with histidine or inserting at least onehistidine into antigen-binding molecules.

In the production methods of the present invention, non-natural aminoacids may be used instead of histidine. Therefore, the present inventioncan also be understood by replacing the above-mentioned histidine withnon-natural amino acids.

Furthermore, in another embodiment, the antigen-binding molecules thatare produced by the production methods described above include, forexample, antigen-binding molecules including modified antibody constantregions. Accordingly, the production methods of the present inventionmay further comprise the step of modifying the amino acids of antibodyconstant regions.

The antigen-binding molecules that are produced by the productionmethods of the present invention are superior in the retention inplasma. Thus, the production methods of the present invention can beused as methods for producing antigen-binding molecules that aresuperior in the retention in plasma.

Furthermore, antigen-binding molecules produced by the productionmethods are expected to be capable of binding to the antigen two or moretimes when administered to animals such as humans, mice, or monkeys.Thus, the production methods of the present invention can be used asmethods for producing antigen-binding molecules that are capable ofbinding to the antigen two or more times.

Furthermore, antigen-binding molecules produced by the productionmethods of the present invention are expected to be capable of bindingto more antigens as compared to the number of their antigen-bindingsites when administered to animals such as humans, mice, or monkeys.Thus, the production methods of the present invention can be used asmethods for producing antigen-binding molecules that are capable ofbinding to more antigens as compared to the number of theirantigen-binding sites.

Furthermore, antigen-binding molecules produced by the productionmethods of the present invention are expected to be capable ofdissociating within a cell from an extracellularly-bound antigen whenadministered to animals such as humans, mice, or monkeys. Thus, theproduction methods of the present invention can be used as methods forproducing antigen-binding molecules that are capable of dissociatingwithin a cell from an extracellularly-bound antigen.

Furthermore, antigen-binding molecules produced by the productionmethods of the present invention are expected to be capable of beingbound to an antigen and internalized into a cell as well as beingreleased to the outside of the cell in an antigen-free form, whenadministered to animals such as humans, mice, or monkeys. Thus, theproduction methods of the present invention can be used as methods forproducing antigen-binding molecules that are capable of being bound toan antigen and internalized into a cell and being released to theoutside of the cell in an antigen-free form.

Furthermore, antigen-binding molecules that are produced by theproduction methods of the present invention are expected to be capableof rapidly eliminating antigens from plasma when administered to animalssuch as humans, mice, or monkeys. Thus, the production methods of thepresent invention can be used as method for producing antigen-bindingmolecules with increased (high) ability to eliminate antigens in plasma.

Furthermore, such antigen-binding molecules can reduce the number ofdoses in patients and are expected to be especially superior aspharmaceuticals. Thus, the production methods of the present inventioncan be used as methods for producing antigen-binding molecules for usedas pharmaceutical compositions.

Genes obtained by the production methods of the present invention aretypically carried by (inserted into) appropriate vectors, and thenintroduced into host cells. The vectors are not particularly limited aslong as they stably retain the inserted nucleic acids. For example, whenEscherichia coli (E. coli) is used as the host, preferred cloningvectors include pBluescript vector (Stratagene); however, variouscommercially available vectors may be used. When using vectors toproduce the antigen-binding molecules of the present invention,expression vectors are particularly useful. The expression vectors arenot particularly limited as long as the vectors express theantigen-binding molecules in vitro, in E. coli, in culture cells, or ina body of an organism. For example, pBEST vector (Promega) is preferredfor in vitro expression; pET vector (Invitrogen) is preferred for E.coli; pME18S-FL3 vector (GenBank Accession No. AB009864) is preferredfor culture cells; and pME18S vector (Mol Cell Biol. 8:466-472 (1988))is preferred for bodies of organisms. DNAs of the present invention canbe inserted into the vectors by conventional methods, for example, byligation using restriction enzyme sites (Current protocols in MolecularBiology, edit. Ausubel et al., (1987) Publish. John Wiley & Sons,Section 11.4-11.11).

The above host cells are not particularly limited, and various hostcells may be used depending on the purpose. Examples of cells forexpressing the antigen-binding molecules include bacterial cells (suchas those of Streptococcus, Staphylococcus, E. coli, Streptomyces, andBacillus subtilis), eukaryotic cells (such as those of yeast andAspergillus), insect cells (such as Drosophila S2 and Spodoptera SF9),animal cells (such as CHO, COS, HeLa, C127, 3T3, BHK, HEK293, and Bowesmelanoma cells), and plant cells. Vectors can be introduced into a hostcell by known methods, for example, calcium phosphate precipitationmethods, electroporation methods (Current protocols in Molecular Biologyedit. Ausubel et al. (1987) Publish. John Wiley & Sons, Section9.1-9.9), lipofection methods, and microinjection methods.

The host cells can be cultured by known methods. For example, when usinganimal cells as a host, DMEM, MEM, RPMI 1640, or IMDM may be used as theculture medium. They may be used with serum supplements such as FBS orfetal calf serum (FCS). The cells may be cultured in serum-freecultures. The preferred pH is about 6 to 8 during the course ofculturing. Incubation is carried out typically at 30 to 40° C. for about15 to 200 hours. Medium is exchanged, aerated, or agitated, asnecessary.

Appropriate secretion signals may be incorporated to polypeptides ofinterest so that the antigen-binding molecules expressed in the hostcell are secreted into the lumen of the endoplasmic reticulum, into theperiplasmic space, or into the extracellular environment. These signalsmay be endogenous to the antigen-binding molecules of interest or may beheterologous signals.

On the other hand, for example, production systems using animals orplants may be used as systems for producing polypeptides in vivo. Apolynucleotide of interest is introduced into an animal or plant and thepolypeptide is produced in the body of the animal or plant, and thencollected. The “hosts” of the present invention include such animals andplants.

The production system using animals include those using mammals orinsects. It is possible to use mammals such as goats, pigs, sheep, mice,and bovines (Vicki Glaser SPECTRUM Biotechnology Applications (1993)).The mammals may be transgenic animals.

For example, a polynucleotide encoding an antigen-binding molecule ofthe present invention is prepared as a fusion gene with a gene encodinga polypeptide specifically produced in milk, such as the goat β-casein.Next, goat embryos are injected with polynucleotide fragments containingthe fusion gene, and then transplanted to female goats. Desiredantigen-binding molecules can be obtained from milk produced by thetransgenic goats, which are born from the goats that received theembryos, or from their offspring. Hormones may be administered asappropriate to increase the volume of milk containing theantigen-binding molecule produced by the transgenic goats (Ebert et al.,Bio/Technology (1994) 12: 699-702).

Insects such as silkworms may be used to produce the antigen-bindingmolecules of the present invention. When silkworms are used,baculoviruses carrying a polynucleotide encoding an antigen-bindingmolecule of interest can be used to infect silkworms, and theantigen-binding molecule of interest can be obtained from their bodyfluids.

Furthermore, when plants are used to produce the antigen-bindingmolecules of the present invention, for example, tobacco may be used.When tobacco is used, a polynucleotide encoding an antigen-bindingmolecule of interest is inserted into a plant expression vector, forexample, pMON 530, and then the vector is introduced into bacteria, suchas Agrobacterium tumefaciens. The bacteria are then allowed to infecttobacco such as Nicotiana tabacum, and the desired antigen-bindingmolecules can be collected from their leaves (Ma et al., Eur. J.Immunol. (1994) 24: 131-138). Alternatively, it is possible to infectduckweed (Lemna minor) with similar bacteria. After cloning, the desiredantigen-binding molecules can be obtained from the duckweed cells (Cox KM et al., Nat. Biotechnol. 2006 December; 24(12):1591-1597).

The thus obtained antigen-binding molecules may be isolated from theinside or outside (such as the medium and milk) of host cells, andpurified as substantially pure and homogenous antigen-binding molecules.The methods for isolating and purifying antigen-binding molecules arenot particularly limited, and isolation and purification methods usuallyused for polypeptide purification can be used. Antigen-binding moleculesmay be isolated and purified, by appropriately selecting and combining,for example, chromatographic columns, filtration, ultrafiltration,salting out, solvent precipitation, solvent extraction, distillation,immunoprecipitation, SDS-polyacrylamide gel electrophoresis, isoelectricfocusing, dialysis, and recrystallization.

Chromatography includes, for example, affinity chromatography, ionexchange chromatography, hydrophobic chromatography, gel filtration,reverse-phase chromatography, and adsorption chromatography (Strategiesfor Protein Purification and Characterization: A Laboratory CourseManual. Ed Daniel R. Marshak et al., (1996) Cold Spring HarborLaboratory Press). Such chromatographic methods can be conducted usingliquid phase chromatography such as HPLC and FPLC. Columns used foraffinity chromatography include, protein A columns and protein Gcolumns. Columns using protein A include, for example, Hyper D, POROS,and Sepharose F. F. (Pharmacia).

If needed, an antigen-binding molecule can be modified arbitrarily, andpeptides can be partially deleted by allowing an appropriate proteinmodification enzyme to act before or after purification of theantigen-binding molecule. Such protein modification enzymes include, forexample, trypsin, chymotrypsin, lysyl endopeptidases, protein kinases,and glucosidases.

<Anti-IL-6 Receptor Antibodies>

Furthermore, the present invention provides the anti-IL-6 receptorantibodies of (a) to (m) below:

-   -   (a) an antibody that includes a heavy chain variable region        including an amino acid sequence, in which at least one of Tyr        at position 27, Asp at position 31, Asp at position 32, Trp at        position 35, Tyr at position 51, Asn at position 59, Ser at        position 63, Met at position 106, and Tyr at position 108 in the        amino acid sequence of SEQ ID NO: 1 (H53 variable region) has        been substituted with His;    -   (b) an antibody that includes a heavy chain variable region        (H3pI) having an amino acid sequence, in which Tyr at position        27, Asp at position 31, and Trp at position 35 in the amino acid        sequence of SEQ ID NO: 1 (H53 variable region) have been        substituted with His;    -   (c) an antibody that includes a heavy chain variable region        having an amino acid sequence, in which Tyr at position 27, Asp        at position 31, Asp at position 32, Trp at position 35, Asn at        position 59, Ser at position 63, and Tyr at position 108 in the        amino acid sequence of SEQ ID NO: 1 (H53 variable region) have        been substituted with His;    -   (d) an antibody that includes a heavy chain variable region        (H170) having an amino acid sequence, in which Tyr at position        27, Asp at position 31, Asp at position 32, Trp at position 35,        Asn at position 59, Ser at position 63, and Tyr at position 108        have been substituted with His, and in which Ser at position 99        has been substituted with Val and Thr at position 103 has been        substituted with Ile in the amino acid sequence of SEQ ID NO: 1        (H53 variable region);    -   (e) an antibody that includes a heavy chain variable region        having an amino acid sequence, in which Asp at position 31, Tyr        at position 51, Ser at position 63, Met at position 106, and Tyr        at position 108 in the amino acid sequence of SEQ ID NO: 1 (H53        variable region) have been substituted with His;    -   (f) an antibody that includes a heavy chain variable region        (CLH5) having an amino acid sequence, in which Asp at position        31, Tyr at position 51, Ser at position 63, Met at position 106,        and Tyr at position 108 have been substituted with His, and in        which Ser at position 99 has been substituted with Phe and Thr        at position 103 has been substituted with Ile in the amino acid        sequence of SEQ ID NO: 1 (H53 variable region);    -   (g) an antibody that includes a light chain variable region        having an amino acid sequence, in which at least one of Asp at        position 28, Tyr at position 32, Glu at position 53, Ser at        position 56, and Asn at position 92 in the amino acid sequence        of SEQ ID NO: 2 (PF1L variable region) has been substituted with        His;    -   (h) an antibody that includes a light chain variable region        (L73) having an amino acid sequence, in which Asp at position        28, Tyr at position 32, and Glu at position 53 in the amino acid        sequence of SEQ ID NO: 2 (PF1L variable region) have been        substituted with His;    -   (i) an antibody that includes a light chain variable region        (L82) having an amino acid sequence, in which Tyr at position 32        and Glu at position 53 in the amino acid sequence of SEQ ID NO:        1 (H53 variable region) have been substituted with His;    -   (j) an antibody that includes a light chain variable region        (CLL5) having an amino acid sequence, in which Tyr at position        32, Glu at position 53, Ser at position 56, and Asn at position        92 in the amino acid sequence of SEQ ID NO: 2 (PF1L variable        region) have been substituted with His;    -   (k) an antibody that includes the heavy chain variable region        of (b) and the light chain variable region of (h);    -   (l) an antibody that includes the heavy chain variable region        of (d) and the light chain variable region of (i); and    -   (m) an antibody that includes the heavy chain variable region        of (f) and the light chain variable region of (h).

Specific examples of the heavy chain variable region having an aminoacid sequence in which at least one of Tyr at position 27, Asp atposition 31, Asp at position 32, Trp at position 35, Tyr at position 51,Asn at position 59, Ser at position 63, Met at position 106, and Tyr atposition 108 in the amino acid sequence of SEQ ID NO: 1 (H53 variableregion) has been substituted with His include, for example, thefollowing heavy chain variable regions.

-   -   a heavy chain variable region having the amino acid sequence of        SEQ ID NO: 3 (H3pI)    -   a heavy chain variable region having the amino acid sequence of        SEQ ID NO: 4 (H170)    -   a heavy chain variable region having the amino acid sequence of        SEQ ID NO: 5 (CLH5)

Specific examples of the light chain variable region having an aminoacid sequence in which at least one of Asp at position 28, Tyr atposition 32, Glu at position 53, Ser at position 56, and Asn at position92 in the amino acid sequence of SEQ ID NO: 2 (PF1L variable region) hasbeen substituted with His include, for example, the following lightchain variable regions.

-   -   a light chain variable region having the amino acid sequence of        SEQ ID NO: 6 (L73)    -   a light chain variable region having the amino acid sequence of        SEQ ID NO: 7 (L82)    -   a light chain variable region having the amino acid sequence of        SEQ ID NO: 8 (CLL5)

The amino acid positions and substitutions in each of theabove-described antibodies H3pI, H170, CLH5, L73, L82, and CLL5 areshown below in Table 1. The amino acid positions are shown based on theKabat numbering.

The present invention provides antibodies comprising at least any one ofthe amino acid substitutions described above in (a) to (j), and methodsfor producing the antibodies. Thus, the antibodies of the presentinvention also include antibodies comprising not only any of the aminoacid substitutions described above in (a) to (j) but also amino acidsubstitution(s) other than those described above in (a) to (j). Aminoacid substitutions other than those described above in (a) to (j)include, for example, substitution, deletion, addition, and/or insertionin the amino acid sequence of CDRs and FRs.

Furthermore, the present invention provides the anti-IL-6 receptorantibodies of (1) to (28) below:

-   -   (1) an antibody that includes the heavy chain variable region        (VH1-IgG1 variable region) having the amino acid sequence from        positions 1 to 119 in SEQ ID NO: 21 (VH1-IgG1);    -   (2) an antibody that includes the heavy chain variable region        (VH2-IgG1 variable region) having the amino acid sequence from        positions 1 to 119 in SEQ ID NO: 22 (VH2-IgG1);    -   (3) an antibody that includes the heavy chain variable region        (VH3-IgG1 variable region) having the amino acid sequence from        positions 1 to 119 in SEQ ID NO: 23 (VH3-IgG1);    -   (4) an antibody that includes the heavy chain variable region        (VH4-IgG1 variable region) having the amino acid sequence from        positions 1 to 119 in SEQ ID NO: 24 (VH4-IgG1);    -   (5) an antibody that includes the light chain variable region        (VL1-CK variable region) having the amino acid sequence from        positions 1 to 107 in SEQ ID NO: 25 (VL1-CK);    -   (6) an antibody that includes the light chain variable region        (VL2-CK variable region) having the amino acid sequence from        positions 1 to 107 in SEQ ID NO: 26 (VL2-CK);    -   (7) an antibody that includes the light chain variable region        (VL3-CK variable region) having the amino acid sequence from        positions 1 to 107 in SEQ ID NO: 27 (VL3-CK);    -   (8) an antibody (Fv1-IgG1) that includes the heavy chain        variable region of (2) and the light chain variable region of        (6);    -   (9) an antibody (Fv2-IgG1) that includes the heavy chain        variable region of (1) and a light chain variable region having        the amino acid sequence of SEQ ID NO: 7 (L82);    -   (10) an antibody (Fv3-IgG1) that includes the heavy chain        variable region of (4) and the light chain variable region of        (5);    -   (11) an antibody (Fv4-IgG1) that includes the heavy chain        variable region of (3) and the light chain variable region of        (7);    -   (12) an antibody (VH3-IgG2 □GK) that includes a heavy chain        having the amino acid sequence of SEQ ID NO: 33;    -   (13) an antibody (VH3-M58) that includes a heavy chain having        the amino acid sequence of SEQ ID NO: 34;    -   (14) an antibody (VH3-M73) that includes a heavy chain having        the amino acid sequence of SEQ ID NO: 35;    -   (15) an antibody (Fv4-IgG2 □GK) that includes the heavy chain        of (12) and a light chain having the amino acid sequence of SEQ        ID NO: 27 (VL3-CK);    -   (16) an antibody (Fv4-M58) that includes the heavy chain of (13)        and a light chain having the amino acid sequence of SEQ ID NO:        27 (VL3-CK);    -   (17) an antibody (Fv4-M73) that includes the heavy chain of (14)        and a light chain having the amino acid sequence of SEQ ID NO:        27 (VL3-CK);    -   (18) an antibody (VH2-M71) that includes a heavy chain having        the amino acid sequence of SEQ ID NO: 36 (VH2-M71);    -   (19) an antibody (VH2-M73) that includes a heavy chain having        the amino acid sequence of SEQ ID NO: 37 (VH2-M73);    -   (20) an antibody (VH4-M71) that includes a heavy chain having        the amino acid sequence of SEQ ID NO: 38 (VH4-M71);    -   (21) an antibody (VH4-M73) that includes a heavy chain having        the amino acid sequence of SEQ ID NO: 39 (VH4-M73);    -   (22) an antibody (Fv1-M71) that includes the heavy chain of (18)        and a light chain having the amino acid sequence of SEQ ID NO:        26 (VL2-CK);    -   (23) an antibody (Fv1-M73) that includes the heavy chain of (19)        and a light chain having the amino acid sequence of SEQ ID NO:        26 (VL2-CK);    -   (24) an antibody (Fv3-M71) that includes the heavy chain of (20)        and a light chain having the amino acid sequence of SEQ ID NO:        25 (VL1-CK);    -   (25) an antibody (Fv3-M73) that includes the heavy chain of (21)        and a light chain having the amino acid sequence of SEQ ID NO:        25 (VL1-CK);    -   (26) an antibody that includes a light chain having the amino        acid sequence of SEQ ID NO: 25 (VL1-CK);    -   (27) an antibody that includes a light chain having the amino        acid sequence of SEQ ID NO: 26 (VL2-CK); and    -   (28) an antibody that includes a light chain having the amino        acid sequence of SEQ ID NO: 27 (VL3-CK).

Furthermore, the present invention provides the FRs and CDRs of (a) to(v) below: (a) the heavy chain CDR1 of SEQ ID NO: 40 (VH1, 2, 3, 4);

-   -   (b) the heavy chain CDR2 of SEQ ID NO: 41 (VH1, 2);    -   (c) the heavy chain CDR2 of SEQ ID NO: 42 (VH3);    -   (d) the heavy chain CDR2 of SEQ ID NO: 43 (VH4);    -   (e) the heavy chain CDR3 of SEQ ID NO: 44 (VH1, 2);    -   (f) the heavy chain CDR3 of SEQ ID NO: 45 (VH3, 4);    -   (g) the heavy chain FR1 of SEQ ID NO: 46 (VH1, 2);    -   (h) the heavy chain FR1 of SEQ ID NO: 47 (VH3, 4):    -   (i) the heavy chain FR2 of SEQ ID NO: 48 (VH1, 2, 3, 4);    -   (j) the heavy chain FR3 of SEQ ID NO: 49 (VH1);    -   (k) the heavy chain FR3 of SEQ ID NO: 50 (VH2);    -   (l) the heavy chain FR3 of SEQ ID NO: 51 (VH3, 4);    -   (m) the heavy chain FR4 of SEQ ID NO: 52 (VH1, 2, 3, 4);    -   (n) the light chain CDR1 of SEQ ID NO: 53 (VL1, 2);    -   (o) the light chain CDR1 of SEQ ID NO: 54 (VL3);    -   (p) the light chain CDR2 of SEQ ID NO: 55 (VL1, VL3);    -   (q) the light chain CDR2 of SEQ ID NO: 56 (VL2);    -   (r) the light chain CDR3 of SEQ ID NO: 57 (VL1, 2, 3);    -   (s) the light chain FR1 of SEQ ID NO: 58 (VL1, 2, 3);    -   (t) the light chain FR2 of SEQ ID NO: 59 (VL1, 2, 3);    -   (u) the light chain FR3 of SEQ ID NO: 60 (VL1, 2, 3); and    -   (v) the light chain FR4 of SEQ ID NO: 61 (VL1, 2, 3).

The respective sequences of the above (a) to (v) are shown in FIG. 25.Furthermore, the present invention provides polypeptides including anyone of the FRs and CDRs of the above (a) to (v).

The anti-IL-6 receptor antibodies of the present invention also includefragments and modified products of antibodies including any of the aminoacid substitutions described above. Such antibody fragments include, forexample, Fab, F(ab′)2, Fv, single chain Fv (scFv) in which Fv of H and Lchains are linked together via an appropriate linker, single domain Hchain and single domain L chain (for example, Nat. Biotechnol. 2005September; 23(9):1126-36), Unibody (WO 2007059782 A1), and SMIP (WO2007014278 A2). The origin of antibodies is not particularly limited.The antibodies include human, mouse, rat, and rabbit antibodies. Theantibodies of the present invention may also be chimeric, humanized,fully humanized antibodies, or such.

Specifically, such antibody fragments are obtained by treatingantibodies with enzymes, for example, papain or pepsin, or byconstructing genes that encode such antibody fragments, inserting theminto expression vectors, and then expressing them in appropriate hostcells (see, for example, Co, M. S. et al., J. Immunol. (1994) 152,2968-2976; Better, M. & Horwitz, A. H. Methods in Enzymology (1989) 178,476-496; Plueckthun, A. & Skerra, A. Methods in Enzymology (1989) 178,497-515; Lamoyi, E., Methods in Enzymology (1989) 121, 652-663;Rousseaux, J. et al., Methods in Enzymology (1989) 121, 663-66; Bird, R.E. et al., TIBTECH (1991) 9, 132-137).

The present invention provides methods of producing (i) a polypeptide ofthe present invention, or (ii) a polypeptide encoded by a gene encodingthe polypeptide of the present invention, wherein the methods comprisethe step of culturing a host cell comprising a vector into which apolynucleotide encoding the polypeptide of the present invention isintroduced.

More specifically, the present invention provides methods of producing apolypeptide of the present invention, which comprise the steps of:

-   -   (a) culturing a host cell comprising a vector into which a gene        encoding the polypeptide of the present invention is introduced;        and    -   (b) obtaining the polypeptide encoded by the gene.

scFv is obtained by linking the V regions of antibody H and L chains. Insuch scFv, the H chain V region is linked to the L chain V region via alinker, preferably a peptide linker (Huston, J. S. et al., Proc. Natl.Acad. Sci. U.S.A. (1988) 10.0, 5879-5883). The H chain and L chain Vregions in an scFv may be derived from any of the antibodies describedabove. The peptide linker to link the V regions includes, for example,arbitrary single chain peptides of 12 to 19 amino acid residues.

When an anti-IL-6 receptor antibody of the present invention includes aconstant region, the constant region may be of any type, for example,IgG1, IgG2, or IgG4 may be used. The constant region is preferably ahuman antibody constant region. Alternatively, the constant region maybe a modified form including substitution, deletion, addition, and/orinsertion in the amino acid sequence of human IgG1, human IgG2, or humanIgG4 constant regions.

Preferred IL-6 receptor to which an anti-IL-6 receptor antibody of thepresent invention binds is human IL-6 receptor.

The anti-IL-6 receptor antibodies of the present invention are superiorin the retention in plasma, and they exist for a prolonged period in theplasma in a form capable of binding to the antigen, i.e., soluble ormembrane-associated IL-6 receptors. Thus, the anti-IL-6 receptorantibodies bind in vivo to soluble or membrane-associated IL-6 receptorsfor a prolonged period. Furthermore, the anti-IL-6 receptor antibodiesare capable of binding to IL-6 receptors twice or more times, and thusassumed to be able to neutralize three or more IL-6 receptors.

<Pharmaceutical Compositions>

The present invention also relates to pharmaceutical compositions thatinclude antigen-binding molecules of the present invention,antigen-binding molecules isolated by the screening methods of thepresent invention, or antigen-binding molecules produced by theproduction methods of the present invention. The antigen-bindingmolecules of the present invention and antigen-binding moleculesproduced by the production methods of the present invention are superiorin the retention in plasma, and thus, expected to reduce theadministration frequency of the antigen-binding molecules, and aretherefore useful as pharmaceutical compositions. The pharmaceuticalcomposition of the present invention may include pharmaceuticallyacceptable carriers.

In the present invention, pharmaceutical compositions ordinarily referto agents for treating or preventing, or testing and diagnosingdiseases.

The pharmaceutical compositions of the present invention can beformulated by methods known to those skilled in the art. For example,they can be used parenterally, in the form of injections of sterilesolutions or suspensions including water or other pharmaceuticallyacceptable liquid. For example, such compositions may be formulated bymixing in the form of unit dose required in the generally approvedmedicine manufacturing practice by appropriately combining withpharmaceutically acceptable carriers or media, specifically with sterilewater, physiological saline, vegetable oil, emulsifier, suspension,surfactant, stabilizer, flavoring agent, excipient, vehicle,preservative, binder, or such. In such formulations, the amount ofactive ingredient is adjusted to obtain an appropriate amount in apre-determined range.

Sterile compositions for injection can be formulated using vehicles suchas distilled water for injection, according to standard formulationpractice.

Aqueous solutions for injection include, for example, physiologicalsaline and isotonic solutions containing dextrose or other adjuvants(for example, D-sorbitol, D-mannose, D-mannitol, and sodium chloride).It is also possible to use in combination appropriate solubilizers, forexample, alcohols (ethanol and such), polyalcohols (propylene glycol,polyethylene glycol, and such), non-ionic surfactants (polysorbate80(TM), HCO-50, and such).

Oils include sesame oil and soybean oils. Benzyl benzoate and/or benzylalcohol can be used in combination as solubilizers. It is also possibleto combine buffers (for example, phosphate buffer and sodium acetatebuffer), soothing agents (for example, procaine hydrochloride),stabilizers (for example, benzyl alcohol and phenol), and/orantioxidants. Appropriate ampules are filled with the preparedinjections.

The pharmaceutical compositions of the present invention are preferablyadministered parenterally. For example, the compositions may be in thedosage form for injections, transnasal administration, transpulmonaryadministration, or transdermal administration. For example, they can beadministered systemically or locally by intravenous injection,intramuscular injection, intraperitoneal injection, subcutaneousinjection, or such.

Administration methods can be appropriately selected in consideration ofthe patient's age and symptoms. The dose of a pharmaceutical compositioncontaining an antigen-binding molecule may be, for example, from 0.0001to 1000 mg/kg for each administration. Alternatively, the dose may be,for example, from 0.001 to 100,000 mg per patient. However, the presentinvention is not limited by the numeric values described above. Thedoses and administration methods vary depending on the patient's weight,age, symptoms, and such. Those skilled in the art can set appropriatedoses and administration methods in consideration of the factorsdescribed above.

Amino acids contained in the amino acid sequences of the presentinvention may be post-translationally modified. For example, themodification of an N-terminal glutamine (Gln) residue into apyroglutamic acid (pGlu) residue by pyroglutamylation is well-known tothose skilled in the art. Naturally, such post-translationally modifiedamino acids are included in the amino acid sequences in the presentinvention.

All prior art documents cited in the specification are incorporatedherein by reference.

EXAMPLES

Herein below, the present invention will be specifically described withreference to Examples, but it is not to be construed as being limitedthereto.

[Example 1] Production of Modified Humanized PM1 Antibody Preparation ofRecombinant Soluble Human IL-6 Receptor (SR344)

A recombinant human IL-6 receptor of the human IL-6 receptor, whichserved an antigen, was prepared as described below. A CHO cell line thatconstantly expresses a soluble human IL-6 receptor (hereinafter referredto as SR344) (Yamasaki, et al., Science 1988; 241: 825-828 (GenBank#X12830)) consisting of the amino acid sequence from the 1st amino acidto the 344th amino acid on the N-terminal side as reported in J.Biochem., 108, 673-676 (1990), was produced.

SR344 was purified from culture supernatant obtained from theSR344-expressing CHO cells using three column chromatographies: BlueSepharose 6 FF column chromatography, affinity chromatography using acolumn in which an antibody specific to SR344 is immobilized, and gelfiltration column chromatography. The fraction that eluted as the mainpeak was used as the final purified product.

Preparation of Recombinant Cynomolgus Monkey Soluble IL-6 Receptor(cIL-6R)

Oligo DNA primers Rhe6Rf1 (SEQ ID NO: 16) and Rhe6Rr2 (SEQ ID NO: 17)were produced based on the publicly-available rhesus monkey IL-6receptor gene sequence (Birney et al., Ensemble 2006, Nucleic AcidsRes., 2006, Jan. 1; 34 (Database issue): D556-61). Using cDNA preparedfrom cynomolgus pancreas as a template, a DNA fragment encoding theentire length of cynomolgus monkey IL-6 receptor gene was prepared byPCR using primers Rhe6Rf1 and Rhe6Rr2. Using the resulting DNA fragmentas a template, a 1131 bp DNA fragment (SEQ ID NO: 20) encoding a proteinin which 6×His is added to the C terminal of the soluble region(Metl-Pro363) containing a signal region of cynomolgus monkey IL-6receptor gene, was amplified by PCR using the oligo DNA primers CynoIL6RN-EcoRI (SEQ ID NO: 18) and CynoIL6R C-NotI-His (SEQ ID NO: 19). Theresulting DNA fragment was digested with EcoRI and NotI and insertedinto a mammalian cell expression vector, and this was then used toproduce a stable expression CHO line (cyno.sIL-6R-producing CHO cells).

A culture medium of cyno.sIL-6R-producing CHO cells was purified with aHisTrap column (GE Healthcare Biosciences), concentrated using AmiconUltra-15 Ultracel-10k (Millipore), and further purified with a Superdex200 pg 16/60 gel filtration column (GE Healthcare Biosciences) to obtainthe final purified product of soluble cynomolgus monkey IL-6 receptor(hereinafter referred to as cIL-6R).

Preparation of Recombinant Cynomolgus Monkey IL-6 (cIL-6)

Cynomolgus monkey IL-6 was prepared as follows. A nucleotide sequenceencoding the 212 amino acids registered under SWISSPROT Accession No.P79341 was produced, cloned into a mammalian cell expression vector, andintroduced into CHO cells to produce a stable expression cell line(cyno.IL-6-producing CHO cells). A culture medium of cyno.IL-6-producingCHO cells was purified with an SP-Sepharose/FF column (GE HealthcareBiosciences), concentrated using Amicon Ultra-15 Ultracel-5k(Millipore), and then further purified with a Superdex 75 pg 26/60 gelfiltration column (GE Healthcare Biosciences). This was concentratedusing Amicon Ultra-15 Ultracel-5k (Millipore) to obtain a final purifiedproduct of cynomolgus monkey IL-6 (hereinafter referred to as cIL-6).

Establishment of Human gp130-Expressing BaF3 Cell Line

A BaF3 cell line expressing human gp130 was established as indicatedbelow in order to obtain a cell line exhibiting IL-6-dependent growth.

Full-length human gp130 cDNA (Hibi et al., Cell 1990; 63: 1149-1157(GenBank #NM_002184)) was amplified by PCR and cloned into theexpression vector pCOS2Zeo, which was prepared by removing the DHFR geneexpression site from pCHOI (Hirata, et al., FEBS Letter 1994; 356:244-248) and inserting a Zeocin resistance gene expression site, toconstruct pCOS2Zeo/gp130. Full-length human IL-6R cDNA was amplified byPCR and cloned into pcDNA3.1(+) (Invitrogen) to constructhIL-6R/pcDNA3.1(+). 10 μg of pCOS2Zeo/gp130 was mixed into BaF3 cells(0.8×10⁷ cells) suspended in PBS, and pulsed using a Gene Pulser(Bio-Rad) at a voltage of 0.33 kV and capacitance of 950 μFD. BaF3 cellshaving undergone gene introduction by electroporation treatment werecultured one whole day and night in RPMI1640 medium (Invitrogen)containing 0.2 ng/mL of mouse interleukin-3 (Peprotech) and 10% fetalbovine serum (hereinafter referred to as FBS, HyClone), and thenscreened by adding RPMI1640 medium containing 100 ng/mL of humaninterleukin-6 (R&D Systems), 100 ng/mL of human interleukin-6 solublereceptor (R&D Systems) and 10% FBS to establish a human gp130-expressingBaF3 cell line (hereinafter referred to as BaF3/gp130). Since thisBaF3/gp130 proliferates in the presence of human interleukin-6 (R&DSystems) and SR344, it can be used to evaluate the growth inhibitoryactivity (namely, IL-6 receptor-neutralizing activity) of anti-IL-6receptor antibody.

Production of Humanized Anti-IL-6 Receptor Antibody

In the context of the instant example and elsewhere herein, the term“wild type” is abbreviated as WT, the term “wild type H chain” isabbreviated as H(WT) (amino acid sequence of SEQ ID NO: 9), and the term“wild type L chain is abbreviated as L(WT) (amino acid sequence: SEQ IDNO. 10). In this context, mutations were introduced into the frameworksequence and CDR sequence of humanized mouse PM1 antibody described inCancer Res. 1993, Feb. 15; 53(4): 851-6, to produce modified H chainsH53 (amino acid sequence: SEQ ID NO: 1) and PF1H (amino acid sequence:SEQ ID NO: 11), and modified L chains L28 (amino acid sequence: SEQ IDNO: 12) and PF1L (amino acid sequence: SEQ ID NO: 2). More specifically,the mutants were produced using the QuikChange Site-Directed MutagenesisKit (Stratagene) according to the method described in the instructionsprovided, and the resulting plasmid fragments were inserted into amammalian cell expression vector to produce the desired H chainexpression vectors and L chain expression vectors. The nucleotidesequences of the obtained expression vectors were determined usingconventional methodologies known to persons skilled in the art.

Expression and Purification of Humanized Anti-IL-6 Receptor Antibody

The antibodies were expressed by the method described below. Humanembryonic kidney cancer-derived HEK293H cell line (Invitrogen) wassuspended in DMEM (Invitrogen) supplemented with 10% Fetal Bovine Serum(Invitrogen). The cells were plated at 10 ml per dish in dishes foradherent cells (10 cm in diameter; CORNING) at a cell density of 5 to6×10⁵ cells/ml and cultured in a CO₂ incubator (37° C., 5% CO₂) for onewhole day and night. Then, the medium was removed by aspiration, and 6.9ml of CHO—S-SFM-II medium (Invitrogen) was added. The prepared plasmidwas introduced into the cells by the lipofection method. The resultingculture supernatants were collected, centrifuged (approximately 2000 g,5 min, room temperature) to remove cells, and sterilized by filteringthrough 0.22-μm filter MILLEX®-GV (Millipore) to obtain thesupernatants. Antibodies were purified from the obtained culturesupernatants by a method known to those skilled in the art usingrProtein A Sepharose™ Fast Flow (Amersham Biosciences). To determine theconcentration of the purified antibody, absorbance was measured at 280nm using a spectrophotometer. Antibody concentrations were calculatedfrom the determined values using an absorbance coefficient calculated bythe PACE method (Protein Science 1995; 4:2411-2423).

[Example 2] Production of pH-Dependently-Binding Antibody H3pI/L73Method for Creating Antibody Capable of Neutralizing Antigen MultipleTimes

Since IgG molecules are divalent, a single IgG molecule can neutralizeup to two antigen molecules when the two sites bind to the antigens;however, it cannot neutralize three or more antigen molecules.Therefore, to maintain the neutralizing effect of a neutralizingantibody over a certain period, it is necessary to administer an amountof the antibody equal to or greater than the amount of antigen producedduring the period. Thus, there is a limitation on the extent to whichthe required dose of antibody can be reduced by improving thepharmacokinetics or affinity of antibody. Therefore, if it were possibleto neutralize two or more antigen molecules with a single IgG molecule,the same dose could improve the duration of neutralizing effect, oralternatively the dose of antibody required to achieve the same durationcould be reduced.

For neutralizing antibodies, there are two types of target antigens:soluble-type antigens, which are present in plasma, and membrane-boundantigens, which are expressed on the surface of cells.

When the antigen is a membrane-bound antigen, an administered antibodybinds to the membrane antigen on the cellular surface, and the antibodyis subsequently taken up into endosomes within the cell byinternalization together with the membrane antigen bound to theantibody. Then, the antibody which is kept bound to the antigen moves toa lysosome where it is degraded by lysosome together with the antigen.The elimination of antibody from the plasma mediated by internalizationby membrane antigen is referred to as antigen-dependent elimination, andthis has been reported for numerous antibody molecules (Drug Discov.Today, 2006 January; 11(1-2): 81-8). Since a single IgG antibodymolecule binds to two antigen molecules when it divalently binds toantigens, and is then internalized and directly degraded by lysosome, asingle ordinary IgG antibody cannot neutralize two or more antigenmolecules (FIG. 1).

The reason for the long retention (slow elimination) of IgG molecules inplasma is that FcRn, known as an IgG molecule salvage receptor,functions (Nat. Rev. Immunol. 2007 September; 7(9): 715-25). IgGmolecules that have been taken up into endosomes by pinocytosis bind toFcRn expressed in endosomes under intraendosomal acidic conditions. IgGmolecules bound to FcRn move to the cell surface where they dissociatefrom FcRn under neutral conditions in plasma and return to plasma, whileIgG molecules unable to bind to FcRn proceed into lysosomes where theyare degraded (FIG. 2).

IgG molecules bound to a membrane antigen are taken up intointracellular endosomes by internalization, move into lysosomes whilebound to the antigen, and undergo degradation. When an IgG antibodydivalently binds to antigens, it neutralizes two antigen molecules andundergoes degradation together with the antigens. If the IgG antibody,when taken up into intracellular endosomes by internalization, candissociate from the antigen under intraendosomal acidic conditions, thedissociated antibody may be able to bind to FcRn expressed in theendosomes. The IgG molecule dissociated from the antigen and bound toFcRn is transferred to the cell surface and then dissociated from FcRnunder neutral conditions in the plasma, thereby return to the plasmaagain. The IgG molecule that has returned to the plasma is able to bindto a new membrane antigen again. The repetition of this process allows asingle IgG molecule to repeatedly bind to membrane antigens, therebyenabling neutralization of a multiple antigens with a single IgGmolecule (FIG. 3).

In the case of a soluble antigen, an antibody administered binds to theantigen in the plasma, and remains in the plasma in the form of anantigen-antibody complex. Normally, while the retention of antibody inplasma is very long (elimination rate is very slow) due to the functionof FcRn as described above, the retention of antigen in plasma is short(elimination rate is fast). Thus, antibody-bound antigens show retentionin plasma comparable to that of antibody (elimination rate is veryslow). Antigens are produced in the body at a constant rate and, in theabsence of antibody, present in plasma at a concentration at which theantigen production rate and the antigen elimination rate are underequilibrium. In the presence of antibody, most of the antigens are boundto antibodies, resulting in the very slow elimination of antigens. Thus,the antigen concentration in plasma increases as compared with that inthe absence of antibody (Kidney Int. 2003, 64, 697-703; J. NationalCancer Institute 2002, 94(19), 1484-1493; J. Allergy and ClinicalImmunology 1997, 100(1), 110-121; Eur. J. Immunol. 1993, 23; 2026-2029).Even if the affinity of antibody for antigen is infinite, antigenconcentration elevates as antibody is slowly eliminated from the plasma,and the neutralizing effect of antibody terminates after theconcentrations of antibody and antigen become equal. Although antibodieswith a stronger dissociation constant (KD) can neutralize solubleantigens at a lower antibody concentration, antibodies at aconcentration half or less than the concentration of antigen present areunable to neutralize antigens regardless of how strong the affinity ofantibody is (Biochem. Biophys. Res. Commun. 2005 Sep. 9; 334(4):1004-13). As is the case with IgG molecules not bound to antigens, IgGmolecules bound to antigens in the plasma are also taken up intoendosomes by pinocytosis, and bind to FcRn expressed in endosomes underintraendosomal acidic conditions. The IgG molecules bound to FcRn movesto the cell surface while the antibody is kept bound to the antigen andthen dissociate from the FcRn under neutral conditions in the plasma.Since the IgG molecules return to the plasma while bound to the antigen,they cannot bind to new antigens in the plasma. In this case, if IgGmolecules can dissociate from the antigen under intraendosomal acidicconditions, the dissociated antigen will not be able to bind to FcRn andthereby may be degraded by lysosomes. On the other hand, the IgGmolecules can return to the plasma again by binding to FcRn. Since theIgG molecules that have returned to the plasma have already dissociatedfrom the antigen in endosomes, they are able to bind to a new antigenagain in the plasma. The repetition of this process allows a single IgGmolecule to repeatedly bind to soluble antigens. This enables a singleIgG molecule to neutralize multiple antigens (FIG. 4).

Thus, regardless of whether the antigen is a membrane antigen or solubleantigen, if the dissociation of IgG antibody from the antigen ispossible under intraendosomal acidic conditions, a single IgG moleculewould be able to repeatedly neutralize antigens. In order for IgGantibodies to dissociate from antigens under intraendosomal acidicconditions, it is necessary that antigen-antibody binding beconsiderably weaker under acidic conditions than under neutralconditions. Since membrane antigens on the cell surface need to beneutralized, antibodies have to strongly bind to antigens at the cellsurface pH, namely pH 7.4. Since the intraendosomal pH has been reportedto be typically pH 5.5 to 6.0 (Nat. Rev. Mol. Cell. Biol. 2004 February;5(2): 121-32), an antibody that weakly binds to an antigen at pH 5.5 to6.0 is considered to dissociate from the antigen under intraendosomalacidic conditions. More specifically, a single IgG molecule thatstrongly binds to an antibody at the cell surface pH of 7.4 and weaklybinds to the antigen at the intraendosomal pH of 5.5 to 6.0 may be ableto neutralize a multiple antigens and thereby improve thepharmacokinetics.

In general, protein-protein interactions consist of hydrophobicinteraction, electrostatic interaction and hydrogen bonding, and thebinding strength is typically expressed as a binding constant (affinity)or apparent binding constant (avidity). pH-dependent binding, whosebinding strength varies between neutral conditions (pH 7.4) and acidicconditions (pH 5.5 to 6.0), is present in naturally-occurringprotein-protein interactions. For example, the above-mentioned bindingbetween IgG molecules and FcRn known as a salvage receptor for IgGmolecules is strong under acidic conditions (pH 5.5 to 6.0) butremarkably weak under neutral conditions (pH 7.4). Most of suchpH-dependently changing protein-protein interactions are associated withhistidine residues. Since the pKa of histidine residue is in thevicinity of pH 6.0 to 6.5, the proton dissociation state of histidineresidues varies between neutral conditions (pH 7.4) and acidicconditions (pH 5.5 to 6.0). Specifically, histidine residues are notcharged and function as hydrogen atom acceptors under neutral conditions(pH 7.4), while they become positively charged and function as hydrogenatom donors under acidic conditions (pH 5.5 to 6.0). It has beenreported that the pH-dependent binding of the above-described IgG-FcRninteraction is also associated with histidine residues present in IgG(Mol. Cell. 2001 April; 7(4): 867-77).

Therefore, pH-dependence can be imparted to protein-protein interactionsby substituting an amino acid residue involved in protein-proteininteractions with a histidine residue, or by introducing a histidineinto an interaction site. Such attempts have also been made inprotein-protein interactions between antibodies and antigens, and amutant antibody with antigen-binding ability decreased under acidicconditions has been successfully acquired by introducing histidine intothe CDR sequence of an anti-egg white lysozyme antibody (FEBS Letter(vol. 309, No. 1, 85-88, 1992)). In addition, an antibody that isprepared by introducing histidine into its CDR sequence and specificallybinds to an antigen at the low pH of cancer tissues but weakly bindsunder neutral conditions has been reported (WO 2003-105757).

Although methods for introducing pH dependency into antigen-antibodyreactions have been reported as described above, an IgG molecule thatneutralizes multiple antigens by strongly binding to antigens at thebody fluid pH of 7.4 but weakly binding to antigens at theintraendosomal pH of pH 5.5 to 6.0 has not been reported. In otherwords, there have been no reports relating to modifications thatsignificantly reduce the binding under acidic conditions whilemaintaining the binding under neutral conditions such that, as comparedto an unmodified antibody, a modified antibody binds to antigensmultiple times in vivo and thereby shows improved pharmacokinetics aswell as improved duration of the neutralizing effect at the same dose.

The IL-6 receptor is present in the body in the form of either solubleIL-6 receptor or membrane IL-6 receptor (Nat. Clin. Pract. Rheumatol.2006 November; 2(11): 619-26). Anti-IL-6 receptor antibodies bind toboth the soluble IL-6 receptor and membrane IL-6 receptor, andneutralize their biological action. It is considered that, after bindingto the membrane IL-6 receptor, anti-IL-6 receptor antibodies are takenup into intracellular endosomes by internalization while bound to themembrane IL-6 receptor, then move into lysosomes while the antibodiesare kept bound to the membrane IL-6 receptor, and undergo degradation bylysosomes together with the membrane IL-6 receptor. In fact, it has beenreported that a humanized anti-IL-6 receptor antibody exhibitsnon-linear clearance, and its antigen-dependent elimination greatlycontributes to the elimination of the humanized anti-IL-6 receptorantibody (The Journal of Rheumatology, 2003, 30; 71426-1435). Thus, onehumanized anti-IL-6 receptor antibody binds to one or two membrane IL-6receptors (monovalently or divalently), and is then internalized anddegraded in lysosomes. Therefore, if it is possible to produce modifiedantibodies that exhibit greatly reduced binding ability under acidicconditions but retain the same binding ability as the wild typehumanized anti-IL-6 receptor antibody under neutral conditions(pH-dependent binding anti-IL-6 receptor antibody), multiple IL-6receptors can be neutralized with a single humanized anti-IL-6 receptorantibody. Thus, in comparison with wild type humanized anti-IL-6receptor antibodies, pH-dependent binding anti-IL-6 receptor antibodiesmay improve the duration of the neutralizing effect in vivo at the samedosage.

Production of pH-Dependently Binding Humanized Anti-IL-6 ReceptorAntibody H3pI/L73:

Introduction of histidine into a CDR has been reported as a method forintroducing pH-dependent binding to antigen-antibody reaction (FEBSLetter (vol. 309, No. 1, 85-88, 1992)). In order to find amino acidresidues exposed on the surface of the variable region of the H53/PF1Lproduced in Example 1 and possible residues interacting with theantigen, a Fv region model of H53/PF1L was created by homology modelingusing MOE software (Chemical Computing Group Inc.). A three-dimensionalmodel constructed on the basis of the sequence information of H53/PF1Lwas used to select H27, H31, H35, L28, L32 and L53 (Kabat numbering,Kabat, E. A. et al., 1991, Sequences of Proteins of ImmunologicalInterest, NIH) as mutation sites that may introduce pH-dependentantigen-binding by histidine introduction. The product in which theresidues at H27, H31 and H35 in H53 produced in Example 1 weresubstituted with histidines was designated as H3pI (amino acid sequence:SEQ ID NO: 3), and the product in which the residues at L28, L32 and L53in PF1L produced in Example 1 were substituted with histidines wasdesignated as L73 (amino acid sequence: SEQ ID NO: 6).

Production, Expression and Purification of H3pI/L73 Expression Vector

Amino acid modification was carried out to produce antibodies modifiedat the selected sites. Mutations were introduced into H53 (nucleotidesequence: SEQ ID NO: 13) and PF1L (nucleotide sequence: SEQ ID NO: 14)produced in Example 1 to produce H3pI (amino acid sequence: SEQ ID NO:3) and L73 (amino acid sequence: SEQ ID NO: 6). More specifically, theQuikChange Site-Directed Mutagenesis Kit (Stratagene) was used accordingto the method described in the instructions provided, and the resultingplasmid fragments were inserted into a mammalian cell expression vectorto produce the desired H chain expression vector and L chain expressionvector. The nucleotide sequences of the resulting expression vectorswere determined using a method known to persons skilled in the art.H3pI/L73 which uses H3pI for the H chain and L73 for the L chain wasexpressed and purified by the method described in Example 1.

[Example 3] Conferring pH-Dependent Antigen Binding Ability by hisModification of CDR Using Phage Display Technology

Production of scFv Molecule of Humanized PM1 Antibody

The humanized PM1 antibody, which is a humanized anti-IL-6R antibody(Cancer Res. 1993 Feb. 15; 53(4): 851-6), was converted into scFv. TheVH and VL regions were amplified by PCR, and humanized PM1 HL scFvhaving the linker sequence GGGGSGGGGSGGGGS (SEQ ID NO. 15) between VHand VL was produced.

Selection of Histidine-Introducible Positions by Histidine Scanning

PCR was performed using the produced humanized PM1 HL scFv DNA as atemplate to produce a histidine library in which any one of the CDRamino acids is replaced with histidine. The library portions wereconstructed by PCR using primers in which the codon of an amino aciddesired to be mutated for the library was replaced with CAT, a codoncorresponding to histidine, and other portions were constructed bynormal PCR. These portions were then linked by assemble PCR. Theconstructed library was digested with SfiI, inserted into a phagemidevector pELBG lad that was also digested with SfiI, and then used totransform XL1-Blue (Stratagene). The resulting colonies were used toevaluate antigen binding by phage ELISA and analyze the sequence of HLscFv. Phage ELISA was carried out using a plate coated with SR344 at 1μg/mL in accordance with J. Mol. Biol. 1992; 227: 381-388. Clones thatwere found to bind to SR344 were subjected to sequence analysis usingspecific primers.

Phage titer was determined by ELISA with an anti-Etag antibody (GEHealthcare) and anti-M13 antibody (GE Healthcare). This value was thenused to select positions where substitution of the CDR residue withhistidine did not significantly alter the binding ability as compared tohumanized PM1 HL scFv, based on the results of phage ELISA for SR344.The selected positions are shown in Table 2. Numbering of each residuewas in accordance with the Kabat numbering (Kabat, et al., 1991,Sequences of Proteins of Immunological Interest, NIH).

TABLE 2 Positions of Histidine Substitution Not Significantly AffectingBinding Ability H31, H50, H54, H56, H57, H58, H59, H60, H61, H62, H63,H64, H65, H100a, H100b, H102 L24, L26, L27, L28, L30, L31, L32, L52,L53, L54, L56, L90, L92, L93, L94

Construction of Histidine-Modified CDR Library

A library was designed in which the amino acids of CDR residues that didnot significantly alter the binding ability when substituted withhistidine as shown in Table 2 (histidine-introducible positions) aretheir original sequence (wild type sequence) or histidine. The librarywas constructed based on the sequences of the H chain PF1H and the Lchain PF1L produced in Example 1 such that the mutated positions for thelibrary have the original sequences or histidines (either the originalsequence or histidines).

The library portions were constructed by PCR using primers that weredesigned such that a position desired to be mutated for the library hasthe original amino acid codon or histidine codon, and other portionswere produced by normal PCR, or by PCR using synthetic primers as in thelibrary portions. These portions were then linked by assemble PCR (J.Mol. Biol. 1996; 256: 77-88).

This library was used to construct a ribosome display library inaccordance with J. Immunological Methods 1999; 231: 119-135. In order tocarry out Escherichia coli cell-free in vitro translation, an SDAsequence (ribosome binding site) and T7 promoter were added to the 5′side, and a gene3 partial sequence serving as a linker for ribosomedisplay was ligated to the 3′ side using SfiI.

Acquisition of pH-Dependent Binding scFv from Library by Bead Panning

In order to concentrate only scFv having the ability to bind to SR344,panning was carried out twice by the ribosome display method inaccordance with Nature Biotechnology 2000 December; 18: 1287-1292. Theprepared SR344 was biotinylated using NHS-PE04-Biotin (Pierce) to obtainan antigen. Panning was carried out using 40 nM of the biotinylatedantigen.

Using the resulting DNA pool as a template, HL scFv was restored by PCRusing specific primers. After digesting with SfiI, the digested HL scFvwas inserted into a phagemide vector pELBG lad that was also digestedwith SfiI, and then used to transform XL1-Blue (Stratagene).

Escherichia coli cells carrying the desired plasmid were grown to 0.4 to0.6 O.D./mL in 2YT medium containing 100 μg/mL ampicillin and 2%glucose. A helper phage (M13KO7, 4.5×10¹¹ pfu) was added thereto,statically cultured for 30 minutes at 37° C., and then cultured withshaking for 30 minutes at 37° C. The culture was transferred to a 50 mLFalcon tube, centrifuged for 10 minutes at 3000 rpm, resuspended in 2YTmedium containing 100 μg/mL ampicillin, 25 μg/mL kanamycin, and 0.5 mMIPTG, and then incubated overnight at 30° C.

The culture incubated overnight was precipitated with 2.5 M NaCl and 10%PEG, and then diluted with PBS to obtain a phage library solution. 10%M-PBS (PBS containing 10% skim milk) and 1 M Tris-HCl were added to thephage library solution to the final concentration of 2.5% M-PBS and pH7.4. Panning was carried out by a typical panning method using anantigen immobilized on magnetic beads (J. Immunol. Methods 2008 Mar. 20;332(1-2): 2-9; J. Immunol. Methods 2001 Jan. 1; 247(1-2): 191-203;Biotechnol. Prog. 2002 March-April; 18(2): 212-20). More specifically,40 pmol of biotin-labeled SR344 was added to the prepared phage libraryand the library was contacted with the antigen for 60 minutes at 37° C.Streptavidin-coated beads (Dynal M-280) washed with 5% M-PBS (PBScontaining 5% skim milk) were added and allowed to bind for 15 minutesat 37° C. The beads were washed five times with both 0.5 ml of PB ST(PBS containing 0.1% TWEEN® 20 polyoxyethelene sorbitan monolaurate, pH7.4) and PBS (pH 7.4). The beads were then suspended in 1 mL of PBS (pH5.5) at 37° C., and the phage was recovered immediately. The recoveredphage solution was added to 10 mL of logarithmic-growth-phase XL1-Blue(OD600 of 0.4 to 0.5) and allowed to stand for 30 minutes at 37° C. forinfection. The infected E. coli were plated onto a 225 mm×225 mm platecontaining 2 YT, 100 μg/mL ampicillin and 2% glucose. These E. coli wereused to begin additional phage culture in the same manner as describedabove and repeat the panning 8 times.

Evaluation by Phage ELISA

The above single colonies were inoculated in 100 μL of 2YT, 100 μg/mLampicillin, 2% glucose and 12.5 μg/mL tetracycline and culturedovernight at 30° C. 2 μL of this culture was inoculated into 300 μL of2YT, 100 μg/mL ampicillin and 2% glucose, and then cultured for 4 hoursat 37° C. A helper phage (M13KO7) was added to the culture at 9×10⁸ pfu,allowed to stand for 30 minutes at 37° C. and then shaken for 30 minutesat 37° C. for infection. Subsequently, the medium was replaced with 300μL of 2 YT, 100 μg/mL ampicillin, 25 μg/mL kanamycin, and 0.5 mM IPTG.After culturing overnight at 30° C., the centrifuged supernatant wasrecovered. 360 μL of 50 mM PBS (pH 7.4) was added to 40 μL of thecentrifuged supernatant and subjected to ELISA. A StreptaWell 96-wellmicrotiter plate (Roche) was coated overnight with 100 μL of PBScontaining 62.5 ng/mL of biotin-labeled SR344. After removing theantigen by washing with PBST, blocking was carried out with 250 μL of 2%BSA-PBS for 1 hour or more. After removing the 2% BSA-PBS, the preparedculture supernatant was added and allowed to stand for 1 hour at 37° C.for antibody binding. After washing, 50 mM PBS (pH 7.4) or 50 mM PBS (pH5.5) was added and incubated by standing for 30 minutes at 37° C. Afterwashing, detection was carried out with an HRP-conjugated anti-M13antibody (Amersham Pharmacia Biotech) diluted with 2% BSA-PBS and TMBsingle solution (Zymed), followed by the addition of sulfuric acid tostop the reaction, and the measurement of absorbance at 450 nm.

However, no clones exhibiting potent pH-dependent binding ability wereobtained by this panning using the antigen immobilized on the magneticbeads. Clones that were found to show weak pH-dependent binding abilitywere subjected to sequence analysis using specific primers. Thepositions in these clones where histidine was present at a high rate areshown in Table 3.

TABLE 3 Positions of Histidine Substitution Detected Using Phage Library(Magnetic Bead Panning) H50, H58, H61, H62, H63, H64, H65, H102 L24,L27, L28, L32, L53, L56, L90, L92, L94Acquisition of pH-Dependently Binding scFv from Library by ColumnPanning

No clones having strong pH-dependent binding ability were obtained bytypical panning using the magnetic bead-immobilized antigen. This may bedue to the following reasons. In the panning using an antigenimmobilized on magnetic beads or a plate, all phages dissociated fromthe magnetic beads or plate under acidic conditions are collected. Thus,phage clones having weak pH dependency recovered together reduce thelikelihood that clones having strong pH dependency are included in thefinally concentrated clones.

Therefore, panning using a column immobilized with an antigen wasexamined as a more stringent panning method (FIG. 5). There have been noprevious reports on the acquisition of clones having pH-dependentbinding ability by using panning with an antigen-immobilized column. Inthe panning using an antigen-immobilized column, when phages that havebeen bound under neutral conditions are eluted under acidic conditions,clones having weak pH dependency rebind to the antigen within the columnand are thereby less eluted, allowing strongly pH-dependent clones thatless rebind within the column to be selectively eluted from the column.In addition, although “all” phages that have dissociated under acidicconditions are recovered in the panning using the antigen immobilized onmagnetic beads or a plate, the panning using a column immobilized withthe antigen enables selective recovery of phages having strongpH-dependent binding ability by allowing an acidic buffer to flowthrough the column to begin the elution and recovering only “appropriatefractions”.

First, a column to which the antigen SR344 was immobilized was prepared.200 μl of Streptavidin Sepharose (GE Healthcare) was washed with 1 ml ofPBS, suspended in 500 μL of PBS, and contacted with 400 pmol ofbiotin-labeled SR344 for 1 hour at room temperature. Subsequently, anempty column (Amersham Pharmacia Biotech) was filled with the abovesepharose and washed with about 3 mL of PBS. The above-mentionedPEG-precipitated library phages were diluted to 1/25 with 0.5% BSA-PBS(pH 7.4), passed through a 0.45 nm filter, and then added to the column.After washing with about 6 mL of PBS (pH 7.4), 50 mM MES-NaCl (pH5.5)was allowed to flow through the column to elute antibodies thatdissociate under low pH. The appropriate eluted fractions werecollected, and the recovered phage solution was added to 10 mL oflogarithmic-growth-phase XL1-Blue (OD600 of 0.4 to 0.5) and allowed tostand for 30 minutes at 37° C.

The infected E. coli were plated onto a 225 mm×225 mm plate containing2YT, 100 μg/mL ampicillin, and 2% glucose. These E. coli were used tobegin additional phage culture in the same manner as described above andrepeat the panning 6 times.

Evaluation by Phage ELISA

The resulting phages were evaluated by phage ELISA. Clones that werefound to have strong pH dependency were subjected to sequence analysisusing specific primers. As a result, several clones showing strongpH-dependent binding as compared to WT were obtained. As shown in FIG.6, clone CL5 (H chain: CLH5, L chain: CLL5) (CLH5: amino acid sequenceof SEQ ID NO: 5, CLL5: amino acid sequence of SEQ ID NO: 8) was found toexhibit particularly strong pH-dependent binding as compared to WT. Itwas thus confirmed that antibodies exhibiting strong pH-dependentbinding, while being unable to be obtained by typical panning using theantigen immobilized onto magnetic beads, can be obtained by panningusing a column immobilized with the antigen. Therefore, panning using anantigen-immobilized column was found to be a highly effective method forobtaining pH-dependently binding antibodies from a library. The aminoacid sequences of the clones showing pH-dependent binding were analyzed,and the positions where histidine was present at a high probability inthe concentrated clones are shown in Table 4.

TABLE 4 Positions of Histidine Substitution found by Phage Library(Column Panning) H31, H50, H58, H62, H63, H65, H100b, H102 L24, L27,L28, L32, L53, L56, L90, L92, L94

[Example 4] Expression and Purification of Histidine-Modified HumanizedIL-6 Receptor Antibody Production, Expression and Purification ofExpression Vector of Histidine-Modified Humanized IL-6 Receptor Antibody

In order to convert clones showing strong pH dependency in phage ELISAto IgG, VH and VL were respectively amplified by PCR, digested withXhol/Nhel and EcoRI, and inserted to a mammalian cell expression vector.The nucleotide sequence of each DNA fragment was determined by a methodknown to persons skilled in the art. CLH5/L73, in which CLH5 was usedfor the H chain and L73 obtained in Example 2 was used for the L chain,was expressed and purified as IgG. Expression and purification werecarried out by the method described in Example 1.

Antibody having even higher pH dependency was produced by combiningmutation sites. Based on the locations where His was concentrated in thephage library as well as the structural information and the like, H32,H58, H62 and H102 in H3pI which was obtained as an H chain in Example 2were substituted with histidine, and H95 and H99 were furthersubstituted with valine and isoleucine, respectively, to produce H170(SEQ ID NO: 4). The variant production was carried out using the methoddescribed in Example 1. In addition, L82 (SEQ ID NO: 7) was produced bysubstituting the 28th histidine of L73, which was produced as an L chainin Example 2, with aspartic acid. The variant production was carried outusing the method described in Example 1. H170/L82, in which H170 wasused for the H chain and L82 was used for the L chain, was expressed andpurified as IgG using the method described in Example 1.

[Example 5] Evaluation of IL-6R-Neutralizing Activity of pH-DependentBinding Antibody Evaluation of Human IL-6 Receptor-Neutralizing Activityof Clones Converted to IgG

The IL-6 receptor-neutralizing activity was evaluated for fourantibodies: humanized PM1 antibody (WT) and H3pI/L73, CLH5/L73 andH170/L82 produced in Examples 2 and 4.

More specifically, the IL-6 receptor-neutralizing activity was evaluatedusing

BaF3/gp130 exhibiting IL-6/IL-6 receptor-dependent growth. BaF3/gp130was washed three times with RPMI1640 medium containing 10% FBS, thensuspended at 5×10⁴ cells/mL in RPMI1640 medium containing 60 ng/mL ofhuman interleukin-6 (Toray), 60 ng/mL of recombinant soluble human IL-6receptor (SR344) and 10% FBS. 50 μL of the suspension was dispensed intoeach of the wells of a 96-well plate (Corning). Next, the purifiedantibody was diluted with RMPI1640 containing 10% FBS, and 50 μl of theantibody was mixed into each well. After culturing for 3 days at 37° C.and 5% CO₂, WST-8 reagent (Cell Counting Kit-8, Dojindo Laboratories)diluted two-fold with PBS was added at 20 μL/well, and then immediatelymeasured for absorbance at 450 nm (reference wavelength: 620 nm) usingthe Sunrise Classic (Tecan). After culturing for 2 hours, absorbance at450 nm was measured again (reference wavelength: 620 nm). The IL-6receptor-neutralizing activity was evaluated based on the change inabsorbance after 2 hours. As a result, as shown in FIG. 7, H3pI/L73,CLH5/L73 and H170/L82 were shown to have equivalent biologicalneutralization activity in comparison with the humanized PM1 antibody(WT).

[Example 6] Biacore™ Surface Plasmon Resonance Analysis ofpH-Dependently Binding Antibody

Analysis of Binding of pH-Dependently Binding Clones to Soluble IL-6Receptor

Kinetic analyses of antigen-antibody reactions at pH 5.8 and pH 7.4 werecarried out using a Biacore™ T100 surface plasmon resonance system (GEHealthcare) on the four antibodies: humanized PM1 antibody (WT) andH3pI/L73, CLH5/L73, and H170/L82 produced in Examples 2 and 4 (buffer:10 mM MES (pH 7.4 or pH 5.8), 150 mM NaCl, and 0.05% TWEEN® 20(polyoxyethelene sorbitan monolaurate)). Various antibodies were boundonto a sensor chip immobilized with recomb-protein A/G (Pierce) by aminecoupling. SR344 adjusted to concentrations of 9.8 to 400 nM was injectedto the chip as an analyte. Association and dissociation of thepH-dependent binding clones to SR344 was observed in real time (FIGS. 8and 9). All the measurements were carried out at 37° C. Association rateconstants k_(a) (1/Ms) and dissociation rate constants k_(d) (1/s) werecalculated using Biacore T100™ Evaluation Software (GE Healthcare), anddissociation constants KD (M) were calculated on the basis of thosevalues (Table 5). Moreover, the ratio of the affinities at pH 5.8 and pH7.4 were calculated for each clone to evaluate pH-dependent binding. Allthe measurements were carried out at 37° C.

As a result of calculating the affinity ratio between pH 5.8 and pH 7.4for each clone, the pH-dependent binding (affinity) of H3pI/L73,H170/L82 and CLH5/L73 to SR344 was 41-fold, 394-fold and 66-fold,respectively, each showing the pH-dependent binding more than 15 timeshigher than WT.

Anti-IL-6 receptor antibodies that strongly bind to the antigen at theplasma pH of 7.4 but weakly bind to the antigen at the intraendosomal pHof 5.5 to 6.0 have not been reported yet. In this study, antibodies wereobtained that retain the biological neutralization activity equivalentto the WT humanized IL-6 receptor antibody and the affinity at pH 7.4,but exhibit the affinity at pH 5.8 that has been specifically loweredmore than 10 times.

Analysis of Binding of pH-Dependently Binding Clones to Membrane IL-6Receptor

Antigen-antibody reactions to membrane IL-6 receptor at pH 5.8 and pH7.4 were observed for the above produced pH-dependent binding clones,using a Biacore T100™ surface plasmon resonance system (GE Healthcare).The binding to membrane IL-6 receptor was evaluated by evaluating thebinding to the IL-6 receptor immobilized onto a sensor chip. SR344 wasbiotinylated according to a method known to persons skilled in the art,and the biotinylated SR344 was immobilized on the sensor chip viastreptavidin by utilizing the affinity between streptavidin and biotin.All the measurements were carried out at 37° C., and the mobile phasebuffer contained 10 mM MES (pH 5.8), 150 mM NaCl and 0.05% TWEEN® 20(polyoxyethelene sorbitan monolaurate). The pH-dependent binding cloneswere injected therein under the condition of pH 7.4 and allowed to bindto SR344 (injection sample buffer: 10 mM MES (pH 7.4), 150 mM NaCl,0.05% TWEEN® 20 (polyoxyethelene sorbitan monolaurate)), and thepH-dependent dissociation of each clone at the mobile phase pH of 5.8was observed (FIG. 10).

The dissociation rate (141/s)) at pH 5.8 was calculated using BiacoreT100™ Evaluation Software (GE Healthcare) by fitting only thedissociation phase at pH 5.8, where 0.5 μg/mL of the sample was bound in10 mM MES (pH 7.4), 150 mM NaCl, and 0.05% TWEEN® 20 (polyoxyethelenesorbitan monolaurate), and dissociated in 10 mM MES (pH 5.8), 150 mMNaCl, and 0.05% TWEEN® 20 (polyoxyethelene sorbitan monolaurate).Similarly, the dissociation rate (k_(d)(1/s)) at pH 7.4 was calculatedusing Biacore T100™ Evaluation Software (GE Healthcare) by fitting onlythe dissociation phase at pH 7.4, where 0.5 μg/mL of the sample wasbound in 10 mM MES (pH 7.4), 150 mM NaCl, and 0.05% TWEEN® 20(polyoxyethelene sorbitan monolaurate), and dissociated in 10 mM MES (pH7.4), 150 mM NaCl, and 0.05% TWEEN® 20 (polyoxyethelene sorbitanmonolaurate). The pH-dependent dissociation rate constant of each cloneis shown in Table 6.

TABLE 6 Comparison of Rate Constant of Dissociation of pH-DependentBinding Clones directed against SR344 from Membrane IL-6 Receptor kd(1/s) kd ratio pH 7.4 pH 5.8 pH 5.8/pH 7.4 WT 4.84E−04 7.15E−04 1.5H3pI/L73 3.44E−04 3.78E−03 11.0 H170/L82 7.70E−04 1.44E−03 1.9 CLH5/L731.04E−03 5.67E−03 5.5

The highest pH dependency of the dissociation ratio was observed inH3pI/L73 followed by CLH5/L73 and H170/L82 in descending order, and eachclone demonstrated higher pH-dependent dissociation from the membraneIL-6 receptor than WT. However, the rank of pH-dependentassociation/dissociation was different between the soluble IL-6 receptorand membrane IL-6 receptor. It was revealed that H170/L82, whichexhibited the highest pH-dependent binding in the analysis of binding tosoluble IL-6 receptor, showed the lowest pH-dependent binding in theanalysis of binding to the membrane IL-6 receptor. In general, it isknown that while IgG molecules monovalently bind to a soluble antigen(affinity), they divalently bind to membrane antigens (avidity). It issuggested that this difference in the binding mode between solubleantigens and membrane antigens influenced the pH-dependent binding ofH170/L82.

[Example 7] Confirmation of Multiple Binding to Antigen by pH-DependentBinding Antibody

As described in Example 2, pH-dependent binding antibodies may be ableto bind to antigens multiple times. Specifically, a pH-dependent bindingantibody that has bound to an antigen is non-specifically taken up intoendosomes, but dissociated from the soluble antigen under theintraendosomal acidic conditions. The antibody binds to FcRn and therebyreturns to the plasma. Since the antibody that has returned to theplasma is not bound to antigen, it is able to bind to a new antigenagain. The repetition of this process enables pH-dependent bindingantibodies to bind to antigens multiple times. However, for IgGantibodies that do not have pH-dependent binding ability, not allantigens are dissociated from the antibodies under the intraendosomalacidic conditions. Thus, such antibodies that have been returned to theplasma by FcRn remain bound to antigen, and therefore cannot bind to newantigens. Consequently, in nearly all cases, each single molecule of IgGantibodies is able to neutralize only two antigens (in the case ofdivalent binding).

Therefore, it was evaluated whether the three pH-dependently bindingantibodies (H3pI/L73, CLH5/L73, and H170/L82) constructed in Examples 2and 4 were able to bind to the antigen SR344 multiple times as comparedto the humanized PM1 antibody (wild type, WT).

A Biacore™ surface plasmon resonance system (GE Healthcare) was used toevaluate that the antibodies binding at pH 7.4 and dissociating at pH5.8 were able to bind to the antigen multiple times. The antibody to beevaluated was bound to a recomb-protein A/G (Pierce)-immobilized sensorchip by the amine coupling method, and a mobile phase of pH 7.4 wasallowed to flow (step 1). SR344 solution adjusted to pH 7.4 was thenallowed to flow as an analyte to bind SR344 to the antibody at pH 7.4(step 2). This binding at pH 7.4 mimics the antigen binding in plasma.Subsequently, buffer adjusted to pH 5.8 alone (not containing SR344) wasadded as an analyte to expose the antigen bound to the antibody toacidic conditions (step 3). This dissociation at pH 5.8 mimics thebinding state of antigen-antibody complexes in endosomes. Subsequently,step 2 was repeated. This mimics the rebinding of antibody that has beenreturned to plasma by FcRn to a new antigen. Subsequently, step 2 wasrepeated to expose the antibody-antigen complex to acidic conditions.Repeating “step 2 to step 3” multiple times at 37° C. as described abovecan mimic the in vivo state in which antibodies are repeatedly taken upfrom the plasma into endosomes by pinocytosis and returned to the plasmaby FcRn (Nat. Rev. Immunol. 2007 September; 7(9): 715-25).

The produced pH-dependent binding clones described above were analyzedusing a Biacore T100™ surface plasmon resonance system (GE Healthcare)for their ability to bind to the antigen SR344 multiple times at pH 5.8and pH 7.4. More specifically, the analysis was carried out as follows.All the measurements were carried out at 37° C. First, the sampleantibodies described above were bound onto a recomb-protein A/G(Pierce)-immobilized sensor chip by amine-coupling, where the mobilephase buffer was 10 mM MES (pH 5.8), 150 mM NaCl, and 0.05% TWEEN® 20(polyoxyethelene sorbitan monolaurate) (step 1). SR344 adjusted to aconcentration of about 40 nM was injected as an analyte for 3 minutes atpH 7.4 and allowed to bind (the buffer for injected SR344 was 10 mM MES(pH 7.4), 150 mM NaCl, and 0.05% TWEEN® 20 (polyoxyethelene sorbitanmonolaurate)) (step 2). Subsequently, the injection of SR344 wasdiscontinued and a mobile phase of pH 5.8 was allowed to flow for about70 seconds to expose the antibody/SR344 complex under acidic conditions(step 3). Ten sets of this binding (step 2)/acidity exposure (step 3)process were continuously repeated to observe the sensorgram inreal-time, which is shown in FIG. 11. WT showed less dissociation ofSR344 during the acidic exposure in step 3, and consequently theproportion of antibody capable of binding to new antigens in thesubsequent step 2 was extremely low. In contrast, it was found that thepH-dependent binding clones, particularly H170/L82 and CLH5/L73,demonstrated so strong dissociation during the acidic exposure in step 3that most of the bound SR344 was dissociated, and therefore nearly allantibodies were able to bind to new antigens in the subsequent step 2.In the 10-set repetition of the binding (step 2) and acidic exposure(step 3), almost all H170/L82 and CLH5/L73 antibodies were able to bindto new antigens in each set.

The obtained sensorgrams were used to calculate the binding amount ofSR344 in each set for each sample using Biacore T100™ EvaluationSoftware (GE Healthcare). The integrated values in the time course ofthe 10 sets are shown in FIG. 12. The integrated RU values obtained atthe 10th set are equivalent to the total amount of antigens bound duringthe ten cycles. The pH-dependent binding clones, particularly H170/L82and CLH5/L73, showed the largest total amounts of bound antigens incomparison with WT, and were demonstrated to be able to repeatedly bindto roughly four times the amount of antigens bound by WT. Accordingly,it was revealed that by conferring pH-dependent binding ability to WT,such antibodies can repeatedly bind to antigens and thereby neutralizemultiple antigens.

[Example 8] PK/PD Test of pH-Dependently-Binding Antibody Using HumanIL-6 Receptor Transgenic Mice

IL-6 receptors are present in the body in both soluble IL-6 receptorform and membrane-type IL-6 receptor form (Nat. Clin. Pract. Rheumatol.2006 November; 2(11): 619-26). Anti-IL-6 receptor antibodies bind tosoluble IL-6 receptors and membrane-type IL-6 receptors and neutralizetheir biological action. It is believed that an anti-IL-6 receptorantibody binds to a membrane-type IL-6 receptor, is subsequently takenup into an endosome within a cell by internalization while the antibodyis kept bound to the membrane-type IL-6 receptor, and then moves to alysosome while still kept bound to the membrane-type IL-6 receptor whereit is degraded by lysosome together with the membrane-type IL-6receptor. If H3pI/L73, CLH5/L73, and H170/L82, which are thepH-dependent-binding IL-6 receptor antibodies evaluated in Example 6,are able to return to plasma via FcRn as a result of dissociation underacidic conditions within endosomes, the antibodies that have returned tothe plasma can bind to antigens again. This enables neutralization ofmultiple membrane-type IL-6 receptors with a single antibody molecule.Whether or not the return to the plasma via FcRn as a result ofdissociation under acidic conditions within endosomes is achieved withthe constructed pH-dependent-binding anti-IL-6 receptor antibodies canbe determined by evaluating whether the pharmacokinetics of theseantibodies are improved as compared with that of WT.

Thus, the pharmacokinetics in human-IL-6-receptor transgenic mice(hIL-6R tg mice, Proc. Natl. Acad. Sci. USA 1995 May 23; 92(11): 4862-6)was evaluated for the four types of antibodies, that is, humanized PM1antibody (wild type: WT) and H3pI/L73, CLH5/L73, and H170/L82constructed in Examples 2 and 4. WT, H3pI/L73, CLH5/L73, or H170/L82 wasadministered by single-dose intravenous administration to hIL-6R tg miceat 25 mg/kg, and blood samples were collected, before administration andover time. Collected blood was immediately centrifuged for 15 minutes at15,000 rpm and 4° C. to obtain plasma. Separated plasma was stored in afreezer set to −20° C. or lower until measurements were carried out.

The measurement of concentration in mouse plasma was carried out byELISA. Samples for calibration curve were prepared at plasmaconcentrations of 6.4, 3.2, 1.6, 0.8, 0.4, 0.2 and 0.1 μg/mL. Thecalibration curve samples and mouse plasma measurement samples weredispensed into an immunoplate (Nunc-Immuno Plate, MaxiSorp (Nalge NuncInternational)) immobilized with anti-human IgG (γ-chain specific)F(ab′)2 (Sigma), and allowed to stand undisturbed for one hour at roomtemperature. Goat anti-human IgG-BIOT (Southern BiotechnologyAssociates) and streptavidin-alkaline phosphatase conjugate (RocheDiagnostics) were sequentially allowed to react, and a chromogenicreaction was carried out by using BluePhos Microwell PhosphataseSubstrates System (Kirkegaard & Perry Laboratories) as substrate.Absorbance at 650 nm was measured with a microplate reader. Theconcentrations in mouse plasma were calculated from the absorbance ofthe calibration curve using the analytical software SOFTmax PRO(Molecular Devices). Time courses of plasma concentrations of WT as wellas H3pI/L73, CLH5/L73, and H170/L82 are shown in FIG. 13.

The pharmacokinetics was improved for all of H3pI/L73, CLH5/L73, andH170/L82 as compared with WT. In particular, the pharmacokinetics ofH3pI/L73 and CLH5/L73 were improved considerably. A wild type anti-IL-6receptor antibody (WT) bound to membrane-type IL-6 receptor is taken upinto an endosome within a cell by internalization, moves to a lysosomewhile the antibody is kept bound to the antigen, and then degraded;therefore, it has a short residence time in the plasma. In contrast,since the pharmacokinetics of the pH-dependent-binding anti-IL-6receptor antibodies were improved considerably, the pH-dependent-bindinganti-IL-6 receptor antibodies were thought to return to the plasma againvia FcRn as a result of dissociation from the antigen, membrane-typeIL-6 receptor, under acidic conditions within endosomes.

Although the pharmacokinetics was improved for all of H3pI/L73,CLH5/L73, and H170/L82 as compared with WT, the effect of prolongingplasma persistence time of H170/L82 was weaker than that of H3pI/L73 andCLH5/L73. Since IgG molecules are thought to normally bind divalently tomembrane-bound antigen, it is thought that anti-IL-6 receptor antibodiesalso bind divalently (avidity) to membrane-type IL-6 receptors and thenare internalized. As indicated in Example 6, the analysis using aBiacore™ surface plasmon resonance system revealed that H170/L82 rapidlydissociated from the IL-6 receptor at pH 5.8 when binding to solubleIL-6 receptor (FIG. 9), but the dissociation rate thereof from the IL-6receptor at pH 5.8 when binding to membrane-type IL-6 receptor wasextremely slow (FIG. 10). From this result, the reason for the weakeffect of prolonging residence time in plasma of H170/L82 is thought tobe that the antibody was unable to adequately dissociate withinendosomes after having been internalized due to its slow dissociation atpH 5.8 when binding to membrane-type IL-6 receptor. Namely, as for thecase relating to membrane antigens, it was determined that in order fora single IgG molecule to neutralize multiple membrane antigens, the pHdependency of dissociation from divalent binding (avidity) is moreimportant than the pH dependency of monovalent binding (affinity).

[Example 9] PK/PD Test of pH-Dependently-Binding Antibody UsingCynomolgus Monkeys

Since the pharmacokinetics of the pH-dependently-binding anti-IL-6receptor antibodies were improved considerably in Example 8, thepH-dependently-binding anti-IL-6 receptor antibodies were thought toreturn to plasma via FcRn as a result of dissociation from the antigen,membrane-type IL-6 receptor, under acidic conditions within endosomes.If antibodies that have returned to the plasma can bind to membrane-typeIL-6 receptors again, neutralization of an antigen, the membrane-typeIL-6 receptor, by pH-dependently-binding anti-IL-6 receptor antibodiesis thought to persist longer than that by the wild-type anti-IL-6receptor antibody, at the same dosage. In addition, since the solubleIL-6 receptor is also present among IL-6 receptors, the duration ofneutralization is thought to be longer for the same dosage with respectto the soluble IL-6 receptor as well.

The pharmacokinetics in cynomolgus monkeys was evaluated for WT andH3pI/L73. WT or H3pI/L73 was administered to cynomolgus monkeys bysingle-dose intravenous administration at 1 mg/kg, and blood sampleswere collected, before administration and over time. Collected blood wasimmediately centrifuged for 15 minutes at 15,000 rpm and 4° C. to obtainplasma. The separated plasma was stored in a freezer set to −20° C. orlower until measurements were carried out.

The measurement of concentration in cynomolgus monkey plasma was carriedout by ELISA. First, anti-human IgG (γ-chain specific) F(ab′)2 fragmentof antibody (Sigma) was dispensed into a Nunc-ImmunoPlate MaxiSorp(Nalge Nunc International) and allowed to stand undisturbed overnight at4° C. to prepare plates immobilized with anti-human IgG. Calibrationcurve samples having plasma concentrations of 3.2, 1.6, 0.8, 0.4, 0.2,0.1 and 0.05 μg/mL and cynomolgus monkey plasma measurement samplesdiluted 100-fold or more were prepared; 200 μL of 20 ng/mL cynomolgusmonkey IL-6R was added to 100 μL of the calibration curve samples andplasma measurement samples; and then, they were allowed to standundisturbed for one hour at room temperature. Subsequently, the sampleswere dispensed into the anti-human IgG-immobilized plate and allowed tostand undisturbed for another one hour at room temperature. BiotinylatedAnti-Human IL-6R Antibody (R&D) was allowed to react for one hour atroom temperature, and then Streptavidin-PolyHRP80 (StereospecificDetection Technologies) was allowed to react for one hour. A chromogenicreaction was carried out by using TMP One Component HRP MicrowellSubstrate (BioFX Laboratories) as substrate, then, the reaction wasstopped with 1N sulfuric acid (Showa Chemical) and the absorbance at 450nm was measured with a microplate reader. The concentrations incynomolgus monkey plasma were calculated from the absorbance of thecalibration curve using the analytical software SOFTmax PRO (MolecularDevices). The time courses of plasma concentrations of WT and H3pI/L73after the intravenous administration are shown in FIG. 14. As a result,the pharmacokinetics of H3pI/L73 was improved considerably in comparisonwith WT in cynomolgus monkeys in the same manner as in human IL-6receptor transgenic mice. Since the pharmacokinetics of apH-dependent-binding anti-IL-6 receptor antibody, H3pI/L73, was improvedconsiderably, H3pI/L73 was thought to return to the plasma via FcRn as aresult of dissociation from the antigen, membrane-type IL-6 receptor,under acidic conditions within endosomes.

In order to evaluate the degree to which cynomolgus monkey membrane-typeIL-6 receptor is neutralized by the intravenous administration of WT andH3pI/L73, the effects of sample antibodies on plasma C-reactive protein(CRP) induced by cynomolgus monkey IL-6 were studied. Since CRP issecreted when IL-6 binds to membrane-type IL-6 receptors, CRP serves asan indicator of neutralization of membrane-type IL-6 receptors.Cynomolgus monkey IL-6 (cyno.IL-6 prepared in Example 1) containing 1%inactivated cynomolgus monkey plasma was administered subcutaneouslyinto lower backs of the animals daily at 5 μg/kg from day 3 to day 10after the administration of WT or H3pI/L73. Blood samples were collectedfrom the saphenous vein immediately before the start of cynomolgusmonkey IL-6 administration (day 3) and after the administration at24-hour intervals (day 4 to day 11), then were separated into plasma.The CRP concentrations of individual animals were measured with Cias RCRP (Kanto Chemical) using an automated analyzer (TBA-120FR, ToshibaMedical Systems). The time courses of CRP concentration upon inductionwith cynomolgus IL-6 with respect to WT and H3pI/L73 are shown in FIG.15. As a result, the duration of CRP suppression was prolongedconsiderably by H3pI/L73 in comparison with WT. On the basis of thisfinding, a pH-dependent-binding anti-IL-6 receptor antibody, H3pI/L73,was thought to return to the plasma via FcRn as a result of dissociationfrom its antigen, membrane-type IL-6 receptor, under acidic conditionswithin endosomes; and neutralize the membrane-type IL-6 receptor byre-binding thereto; and thereby suppress production of CRP for a longerperiod of time than WT. In other words, H3pI/L73 was shown to be able tobind to and neutralize the membrane-type IL-6 receptor more than once,as a single antibody molecule. Since the duration of suppression of CRPproduction by H3pI/L73 is prolonged in comparison to that by WT, theduration of time where an antigen, the membrane-type IL-6 receptor, isbound by antibodies was indicated to be prolonged for H3pI/L73 than WT.

In order to evaluate the degree to which cynomolgus monkey soluble IL-6receptor is neutralized by the intravenous administration of WT andH3pI/L73, the concentration of unbound cynomolgus monkey soluble IL-6receptor in cynomolgus monkey plasma was measured. All IgG-typeantibodies (cynomolgus monkey IgG, anti-human IL-6 receptor antibody,and a complex of anti-human-IL-6 receptor antibody and cynomolgus monkeysoluble IL-6 receptor) present in the plasma were adsorbed to Protein Aby adding 30 μL of cynomolgus monkey plasma to an appropriate amount ofrProtein A Sepharose Fast Flow (GE Healthcare) resin dried in a 0.22 μmfilter cup (Millipore). After spinning down with a high-speedcentrifuge, the solution that passed through (hereinafter referred to as“pass solution”) was recovered. Since the pass solution does not containthe complex of anti-human IL-6 receptor antibody and cynomolgus monkeysoluble IL-6 receptor which is bound to protein A, the concentration ofunbound soluble IL-6 receptor can be measured by measuring theconcentration of cynomolgus monkey soluble IL-6 receptor in the passsolution. Monoclonal Anti-human IL-6R Antibody (R&D) that wasruthenium-labeled with Sulfo-Tag NHS Ester (Meso Scale Discovery) andBiotinylated Anti-human IL-6R Antibody (R&D) were mixed with cynomolgusmonkey IL-6 receptor calibration curve samples adjusted toconcentrations of 4000, 2000, 1000, 500, 250, 125, and 62.5 pg/mL andthe plasma samples treated with Protein A as described above. Themixtures were allowed to react for one hour at room temperature.Subsequently, the mixtures were dispensed into an SA-Coated StandardMA2400 96-well plate (Meso Scale Discovery). After allowing to react foranother one hour and washing, Read Buffer T (×4) (Meso Scale Discovery)was dispensed. Immediately thereafter, the measurement with SectorImager 2400 (Meso Scale Discovery) was conducted. The concentrations ofcynomolgus monkey IL-6 receptor were calculated from the response of thecalibration curve by using the analytical software, SOFTmax PRO(Molecular Devices). The time courses of concentrations of unboundcynomolgus monkey soluble IL-6 receptor for WT and H3pI/L73 are shown inFIG. 16. As a result, the duration of neutralization of cynomolgusmonkey soluble IL-6 receptor by H3pI/L73 was considerably prolonged ascompared to that by WT. On the basis of this finding, thepH-dependent-binding anti-IL-6 receptor antibody H3pI/L73 was thought todissociate from its antigen, soluble IL-6 receptor, under acidicconditions in endosomes; and return to the plasma via FcRn; and bind toand neutralize the soluble IL-6 receptor again. Since the duration ofsuppression of unbound cynomolgus monkey soluble IL-6 receptor byH3pI/L73 is prolonged in comparison to that by WT, the duration of timewhere an antigen, the soluble IL-6 receptor, is bound by antibodies wasindicated to be prolonged for H3pI/L73 than WT.

From these findings, the time until the antibody disappears from theplasma as well as the time where soluble and membrane-type IL-6receptors are bound by the antibody in the body were found to beconsiderably elongated for the pH-dependent-binding anti-IL-6 receptorantibodies that were made to bind strongly to the antigen at pH 7.4,which is the pH in the plasma, but bind weakly to the antigen at pH 5.8,which is the pH within endosomes, as compared to the wild-type anti-IL-6receptor antibody. This makes it possible to reduce the dosage andfrequency of administration to patients, and in consequence, the totaladministration dosage. Therefore, the pH-dependent-binding anti-IL-6receptor antibody is thought to be particularly advantageous as apharmaceutical for use as an IL-6 antagonist.

[Example 10] Improvement of pH-Dependent Binding to Membrane-Type IL-6Receptor by Optimization of Variable Region Optimization of VariableRegions H3pI/L73 and CLH5/L82

Antibodies having pH-dependent binding abilities were shown todemonstrate superior effects in Example 9. Therefore, to further improvethe pH-dependent binding abilities, mutations were introduced into theCDR sequence of CLH5 obtained in Example 3 to construct VH1-IgG1 (SEQ IDNO: 21) and VH2-IgG1 (SEQ ID NO: 22). In addition, mutations wereintroduced into the framework sequence and CDR sequence of H3pI toconstruct the modified H chains VH3-IgG1 (SEQ ID NO: 23) and VH4-IgG1(SEQ ID NO: 24). Mutations were introduced into the CDR sequences of L73and L82 to construct the modified L chains VL1-CK (SEQ ID NO: 25),VL2-CK (SEQ ID NO: 26), and VL3-CK (SEQ ID NO: 27). More specifically,the mutants were constructed using the QuikChange Site-DirectedMutagenesis Kit (Stratagene) according to the method described in theappended instructions, and the resulting plasmid fragments were insertedinto an mammalian cell expression vector to construct the desired Hchain expression vectors and L chain expression vectors. The nucleotidesequences of the resulting expression vectors were determined by methodsknown to persons with ordinary skill in the art.

The antibody having VH2-IgG1 (SEQ ID NO: 22) as H chain and VL2-CK (SEQID NO: 26) as L chain was denoted as Fv1-IgG1, the antibody havingVH1-IgG1 (SEQ ID NO: 21) as H chain and L82 as L chain was denoted asFv2-IgG1, the antibody having VH4-IgG1 (SEQ ID NO: 24) as H chain andVL1-CK (SEQ ID NO: 25) as L chain was denoted as Fv3-IgG1, and theantibody having VH3-IgG1 (SEQ ID NO: 23) as H chain and VL3-CK (SEQ IDNO: 27) as L chain was denoted as Fv4-IgG1. Of these, Fv2-IgG1 andFv4-IgG1 were expressed and purified. The expression and purificationwere carried out by the method described in Example 1.

Analysis of Binding of pH-Dependent-Binding Clones to Soluble IL-6Receptor

Kinetic analyses of antigen-antibody reactions at pH 7.4 were carriedout on the four types of antibodies, i.e., the humanized PM1 antibody(wild type: WT), and WT, H3pI/L73-IgG1, Fv2-IgG1, and Fv4-IgG1constructed in Examples 2 and 10, by using a Biacore T100™ surfaceplasmon resonance system (GE Healthcare) (buffer: 10 mM MES (pH 7.4),150 mM NaCl, 0.05% TWEEN® 20 (polyoxyethelene sorbitan monolaurate)).Each antibody was bound on a sensor chip on which an anti-IgG γ chainspecific F(ab)₂ (Pierce) was immobilized by amine coupling, and then,SR344 adjusted to a concentration of 9.8 to 40 nM was injected theretoas an analyte. The association to and dissociation from SR344 wereobserved on a real-time basis for the pH-dependent-binding clones. Allthe measurements were carried out at 37° C. Association rate constantsk_(a) (1/Ms) and dissociation rate constants k_(d). (1/s) werecalculated using Biacore T100™ Evaluation Software (GE Healthcare), anddissociation constants KD (M) were calculated on the basis of thosevalues (Table 7).

TABLE 7 Comparison of Dissociation Rate Constants ofpH-Dependent-Binding Clones from Soluble IL-6 Receptor, SR344 Samplek_(a) (1/Ms) k_(d) (1/s) KD (M) WT 4.0E+05 1.1E−03 2.7E−09 H3pI/L734.1E+05 5.9E−04 1.4E−09 Fv2-IgG1 3.9E+05 7.7E−04 2.0E−09 Fv4-IgG17.2E+05 1.0E−03 1.4E−09

As a result of calculating the affinity at pH 7.4 for each clone, thedissociation constants (affinity, KD value) of WT, H3pI/L73-IgG1,Fv2-IgG1, and Fv4-IgG1 to SR344 were, respectively, 2.7 nM, 1.4 nM, 2.0nM, and 1.4 nM, and they are nearly equivalent. Fv2-IgG1 and Fv4-IgG1were demonstrated to have binding ability to the soluble IL-6 receptorthat is equal to or greater than that of WT.

Analysis of Binding of pH-Dependent-Binding Clones to Membrane-Type IL-6Receptor

Antigen-antibody reactions to membrane-type IL-6 receptor were observedat pH 5.8 and pH 7.4 for the four types of constructed clones, WT,H3pI/L73-IgG1, Fv2-IgG1, and Fv4-IgG1 by using a Biacore T100™ surfaceplasmon resonance system (GE Healthcare). Binding to the membrane-typeIL-6 receptor was evaluated by evaluating binding to the IL-6 receptorimmobilized on a sensor chip. SR344 was biotinylated in accordance witha method known among persons with ordinary skill in the art, and thebiotinylated SR344 was immobilized on the sensor chip via streptavidinusing the affinity between streptavidin and biotin. All the measurementswere carried out at 37° C. The mobile phase buffer was 10 mM MES (pH5.8), 150 mM NaCl and 0.05% TWEEN® 20 (polyoxyethelene sorbitanmonolaurate). The pH-dependent-binding clones were injected thereinunder conditions of pH 7.4 to allow them to bind to SR344 (injectionsample buffer: 10 mM MES (pH 7.4), 150 mM NaCl, 0.05% TWEEN® 20(polyoxyethelene sorbitan monolaurate)), then, pH-dependent dissociationof each clone was observed at the pH of the mobile phase of 5.8 (FIG.17).

Sample concentrations were adjusted to 0.25 μg/mL. Binding was carriedout in 10 mM MES (pH 7.4), 150 mM NaCl, and 0.05% TWEEN® 20(polyoxyethelene sorbitan monolaurate). Dissociation was carried out in10 mM MES (pH 5.8), 150 mM NaCl, and 0.05% TWEEN® 20 (polyoxyethelenesorbitan monolaurate). For this case, the dissociation rate constants(141/s)) at pH 5.8 were calculated by fitting only the dissociationphase at pH 5.8 using Biacore T100™ Evaluation Software (GE Healthcare).In a similar manner, sample concentrations were adjusted to 0.25 μg/mL,binding was carried out in 10 mM MES (pH 7.4), 150 mM NaCl, and 0.05%TWEEN® 20 (polyoxyethelene sorbitan monolaurate), dissociation wascarried out in 10 mM MES (pH 7.4), 150 mM NaCl, and 0.05% TWEEN® 20(polyoxyethelene sorbitan monolaurate), and the dissociation rateconstants (k_(d)(1/s)) at pH 7.4 were calculated by fitting only thedissociation phase at pH 7.4 using Biacore T100™ Evaluation Software (GEHealthcare). The pH-dependent dissociation rate constants of each cloneare shown in Table 8.

TABLE 8 Comparison of Dissociation Rate Constants ofpH-Dependent-Binding Clones from Membrane-Type IL-6 Receptor, SR344 pH7.4 pH 5.8 pH Dependency Sample kd (1/s) kd (1/s) kd (pH 5.8)/kd (pH7.4) WT 2.5E−04 2.5E−04 1.00 H3pI/L73 2.6E−04 6.7E−04 2.59 Fv2-IgG13.4E−04 2.4E−03 7.18 Fv4-IgG1 4.7E−04 2.6E−03 5.56

As a result of calculating pH dependency for each clone, the pHdependencies of binding to the membrane-type IL-6 receptor of the fourclones, WT, H3pI/L73-IgG1, Fv2-IgG1, and Fv4-IgG1 with respect to SR344were 1.0-fold, 2.59-fold, 7.18-fold, and 5.56-fold, respectively.Fv2-IgG1 and Fv4-IgG1 demonstrated higher pH-dependency in dissociationfrom the membrane-type IL-6 receptor than H3pI/L73-IgG1.

On the basis of the above, Fv2-IgG1 and Fv4-IgG1 were shown todemonstrate stronger pH-dependent binding to the membrane-type IL-6receptor than H3pI/L73-IgG1 while maintaining the affinity for thesoluble IL-6 receptor equal to or stronger than that of WT.

[Example 11] PK/PD Test of pH-Dependent-Binding Antibodies withOptimized Variable Regions Using Human IL-6 Receptor Transgenic Mice

The pharmacokinetics of Fv2-IgG1 and Fv4-IgG1, as well as WT andH3pI/L73-IgG1 prepared and evaluated in Example 10 were evaluated usingthe human IL-6 receptor transgenic mice used in Example 8. WT,H3pI/L73-IgG1, Fv2-IgG1, or Fv4-IgG1 was administered by single-doseintravenous administration to hIL-6R tg mice at 25 mg/kg, and theconcentration of each antibody in the plasma was measured in the samemanner as in Example 8. The time courses of the plasma concentrations ofWT, H3pI/L73-IgG1, Fv2-IgG1, and Fv4-IgG1 are shown in FIG. 18.

The pharmacokinetics of H3pI/L73-IgG1 improved in comparison with WT inthe same manner as in Example 8, while the pharmacokinetics of Fv2-IgG1and Fv4-IgG1 was further improved than H3pI/L73-IgG1. Measurement as tothe unbound IL-6 receptor concentrations, as measured in cynomolgusmonkeys in Example 9, was carried out in the hIL-6R tg mice in this testusing the same method. As a result, prolongation of the duration ofneutralization of the soluble IL-6 receptor was confirmed for Fv2-IgG1and Fv4-IgG1 in comparison to that for H3pI/L73-IgG1 (data not shown).As indicated in Example 10, the pH-dependent binding to themembrane-type IL-6 receptor was improved for Fv2-IgG1 and Fv4-IgG1 ascompared with H3pI/L73-IgG1. Therefore, it was indicated that furtherimprovement in the pharmacokinetics and duration of neutralization ofthe soluble IL-6 receptor over those of H3pI/L73-IgG1 is possible byimproving the pH-dependent binding to the membrane-type IL-6 receptor.

[Example 12] Improvement of pH-Dependent Binding to Membrane-Type IL-6Receptor by Optimization of Constant Region Optimization of ConstantRegion of Fv4-IgG1

Generally, binding to membrane-bound antigens has been reported to varydepending on the constant region of the antibody (J. Immunol. Methods1997 Jun. 23; 205(1): 67-72). The constant regions of thepH-dependent-binding antibodies prepared above were of the IgG1 isotype.Therefore, a study was made for optimization of the constant region inorder to improve the pH-dependent binding to the membrane-type IL-6receptor.

A mutation was introduced into a naturally-occurring constant region,i.e., constant region IgG2 (SEQ ID NO: 28), to construct constant regionIgG2ΔGK (SEQ ID NO: 29). Another mutation was introduced into theconstant region IgG2ΔGK to construct constant region M58 (SEQ ID NO:30). Mutations were further introduced into the constant regions IgG2and M58 to construct constant regions M71 (SEQ ID NO: 31) and M73 (SEQID NO: 32).

VH3-IgG2ΔGK (SEQ ID NO: 33) was constructed by substituting the constantregion of VH3-IgG1 prepared in Example 10 with IgG2ΔGK, VH3-M58 (SEQ IDNO: 34) was constructed by substituting the constant region with M58,and VH3-M73 (SEQ ID NO: 35) was constructed by substituting the constantregion with M73. More specifically, expression vectors in which theconstant region portion of VH3 used in Example 10 was substituted by adesired constant region by Nhel/NotI digestion and ligation wereconstructed. The nucleotide sequences of the resulting expressionvectors were determined using a method known among persons with ordinaryskill in the art.

Expression and purification were carried out for the following: Fv4-IgG2using VH3-IgG2ΔGK (SEQ ID NO: 33) for the H chain and VL3-CK (SEQ ID NO:27) for the L chain; Fv4-M58 using VH3-M58 (SEQ ID NO: 34) for the Hchain and VL3-CK (SEQ ID NO: 27) for the L chain; and Fv4-M73 usingVH3-M73 (SEQ ID NO: 35) for the H chain and VL3-CK (SEQ ID NO: 27) forthe L chain. Expression and purification were carried out using themethod described in Example 1.

Analysis of Binding of Fv4 Having Optimized Constant Region to SolubleIL-6 Receptor

The association with and dissociation from SR344 were observed on areal-time basis using the same method as Example 10 for thus-preparedFv4-IgG1, Fv4-IgG2, Fv4-M58, and Fv4-M73 as well as WT. The associationrate constants k_(a) (1/Ms) and dissociation rate constants k_(d) (1/s)were calculated after analysis in the same manner, and then,dissociation constants KD (M) were calculated on the basis of thosevalues (Table 9).

TABLE 9 Comparison of Dissociation Rate Constants ofpH-Dependently-Binding Clones from Soluble IL-6 Receptor, SR344 Sampleka (1/Ms) kd (1/s) KD (M) Fv4-IgG1 7.2E+05 1.0E−03 1.4E−09 Fv4-IgG29.6E+05 1.2E−03 1.3E−09 Fv4-M58 8.3E+05 1.1E−03 1.4E−09 Fv4-M73 7.5E+051.0E−03 1.4E−09

As a result of calculating the affinity at pH 7.4 for each clone, thedissociation constants (affinity, KD value) of Fv4-IgG1, Fv4-IgG2,Fv4-M58, and Fv4-M73 to SR344 were 1.4 nM, 1.3 nM, 1.4 nM, and 1.4 nM,respectively, and they are almost equivalent. This indicates that thebinding ability of pH-dependent-binding clones to the soluble IL-6receptor, SR344, does not change even after modifying the constantregion. On the basis of this finding, the binding ability to the solubleIL-6 receptor was thought to not change for Fv1, Fv2, and Fv3 even ifthe constant region was similarly modified.

Analysis of Binding of Fv4 Having Optimized Constant Region toMembrane-Type IL-6 Receptor

Antigen-antibody reactions to the membrane-type IL-6 receptor at pH 5.8and pH 7.4 were observed for thus-prepared Fv4-IgG1, Fv4-IgG2, Fv4-M58,and Fv4-M73 as well as WT, in the same manner as in Example 10 using aBiacore T100™ surface plasmon resonance system (GE Healthcare). Theresults obtained by injecting the pH-dependent-binding clones under theconditions of pH 7.4 to allow binding to SR344, and by observing thepH-dependent dissociation of each clone in the pH 5.8 mobile phase, areshown in FIG. 19. Further analyses were conducted in the same manner asin Example 10, and the pH-dependent dissociation rates for each cloneare shown in Table 10.

TABLE 10 Comparison of Dissociation Rate Constants ofpH-Dependently-Binding Clones from Membrane-Type IL-6 Receptor, SR344 pH7.4 pH 5.8 pH Dependency Sample kd (1/s) kd (1/s) kd (pH 5.8)/kd (pH7.4) Fv4-IgG1 4.7E−04 2.6E−03 5.56 Fv4-IgG2 1.0E−03 1.8E−02 16.99Fv4-M58 5.4E−04 9.5E−03 17.64 Fv4-M73 5.1E−04 5.1E−03 10.06

As a result of calculating the pH dependency for each clone, the pHdependencies of Fv4-IgG1, Fv4-IgG2, Fv4-M58, and Fv4-M73 to SR344 were5.6-fold, 17.0-fold, 17.6-fold, and 10.1-fold, respectively; thus,Fv4-IgG2, Fv4-M58, and Fv4-M73 all demonstrated higher pH-dependentdissociation from the membrane-type IL-6 receptor than Fv4-IgG1.

Based on the results of analyzing binding to the soluble IL-6 receptorand binding to the membrane-type IL-6 receptor using the variable regionof Fv4, it was found that substitution of the constant region from IgG1to IgG2, M58, or M73 could improve the pH-dependent binding to themembrane-type IL-6 receptor, without causing a change in the affinity tothe soluble IL-6 receptor. This was considered to similarly hold forFv1, Fv2, and Fv3.

[Example 13] PK/PD Test of pH-Dependently-Binding Antibodies HavingOptimized Constant Region Using Human IL-6 Receptor Transgenic Mice

The pharmacokinetics of Fv4-IgG1, Fv4-IgG2, and Fv4-M58 prepared inExample 13 were evaluated using the human IL-6 receptor transgenic mice(hIL-6R tg mice) used in Example 8 to examine the effects of theconstant region on the pharmacokinetics. WT, Fv4-IgG1, Fv4-IgG2, orFv4-M58 was administered to the hIL-6R tg mice by single-doseintravenous administration at 25 mg/kg, and then, measurement of theplasma concentrations of each antibody was carried out in the samemanner as in Example 8. The time courses of plasma concentrations of WT,Fv4-IgG1, Fv4-IgG2, and Fv4-M58 are shown in FIG. 20.

Similar to Example 11, the pharmacokinetics of Fv4-IgG1 was improved incomparison with WT, and the pharmacokinetics of Fv4-IgG2 and Fv4-M58 wasfurther improved in comparison with Fv4-IgG1. Measurement as to theunbound IL-6 receptor concentrations, as measured in cynomolgus monkeysin Example 9, was carried out in the hIL-6R tg mice in this test usingthe same method. As a result, prolongation of the duration ofneutralization of the soluble IL-6 receptor was confirmed for Fv4-IgG2and Fv4-M58 in comparison to that of Fv4-IgG1 (data not shown). Asindicated in Example 10, the pH-dependent binding to the membrane-typeIL-6 receptor was improved for Fv4-IgG2 and Fv4-M58 as compared withFv4-IgG1. Therefore, it was shown that improvement in the pH-dependentbinding to the membrane-type IL-6 receptor and improvement in thepharmacokinetics and duration of neutralization of the soluble IL-6receptor are possible by substituting the constant region from IgG1 toIgG2 or M58. On the basis of this finding, it was thought that thepharmacokinetics and duration of neutralization of the soluble IL-6receptor, not only in the case of Fv4, but also in the cases of FIT 1,Fv2, and Fv3, can be improved as compared to IgG1 by substituting theconstant region from IgG1 to IgG2 or M58.

[Example 14] Construction of pH-Dependently-Binding Antibodies HavingOptimized Variable and Constant Regions

VH2-M71 (SEQ ID NO: 36) and VH2-M73 (SEQ ID NO: 37), having M71 and M73for the constant region of VH2-IgG1, and VH4-M71 (SEQ ID NO: 38) andVH4-M73 (SEQ ID NO: 39), having M71 and M73 for the constant region ofVH4-IgG1, were constructed using the same method as described above.

Fv1-M71 using VH2-M71 for the H chain and VL2-CK for the L chain,Fv1-M73 using VH2-M73 for the H chain and VL2-CK for the H chain,Fv3-M71 using VH4-M71 for the H chain and VL1-CK for the L chain, andFv3-M73 using VH4-M73 for the H chain and VL1-CK for the L chain, wereexpressed and purified. Expression and purification were carried outusing the method described in Example 1.

Analyses of Binding of pH-Dependent-Binding Antibodies Having OptimizedVariable and Constant Regions to Soluble IL-6 Receptor

The association to and dissociation from SR344 were observed on areal-time basis using the same method as Example 10 for the eleven typesof antibodies, humanized PM1 antibody (wild type: WT) and H3pI/L73-IgG1,Fv1-M71, Fv1-M73, Fv2-IgG1, Fv3-M71, Fv3-M73, Fv4-IgG1, Fv4-IgG2,Fv4-M58, and Fv4-M73, constructed as described above. The associationrate constants k_(a) (1/Ms) and dissociation rate constants k_(d). (1/s)were calculated by analysis in the same manner, and the dissociationconstants KD (M) were calculated on the basis of those values (Table11).

TABLE 11 Comparison of Dissociation Rate Constants ofpH-Dependently-Binding Clones from Soluble IL-6 Receptor, SR344 Samplek_(a) (1/Ms) k_(d) (1/s) KD (M) WT 4.0E+05 1.1E−03 2.7E−09 H3pI/L734.1E+05 5.9E−04 1.4E−09 Fv1-M71 5.5E+05 5.4E−04 9.7E−10 Fv1-M73 6.1E+055.5E−04 9.1E−10 Fv2-IgG1 3.9E+05 7.7E−04 2.0E−09 Fv3-M71 7.8E+05 8.2E−041.1E−09 Fv3-M73 8.5E+05 8.7E−04 1.0E−09 Fv4-IgG1 7.2E+05 1.0E−03 1.4E−09Fv4-IgG2 9.6E+05 1.2E−03 1.3E−09 Fv4-M58 8.3E+05 1.1E−03 1.4E−09 Fv4-M737.5E+05 1.0E−03 1.4E−09

All of the resulting ten types of pH-dependent-binding clones were foundto have dissociation constants (affinity, KD values) to the soluble IL-6receptor equal to or stronger than that of WT.

Analyses of Binding of pH-Dependently-Binding Antibodies HavingOptimized Variable and Constant Regions to Membrane-Type IL-6 Receptor

Antigen-antibody reactions to the membrane-type IL-6 receptor at pH 5.8and pH 7.4 were observed in the same manner as in Example 10 using aBiacore T100™ surface plasmon resonance system (GE Healthcare) for theeleven types of antibodies, humanized PM1 antibody (wild type: WT) andH3pI/L73-IgG1, Fv1-M71, Fv1-M73, Fv2-IgG1, Fv3-M71, Fv3-M73, Fv4-IgG1,Fv4-IgG2, Fv4-M58, and Fv4-M73, prepared as described above. ThepH-dependently-binding clones were injected under the condition of pH7.4 to allow them to bind to SR344, and then, the pH-dependentdissociation of each clone at the pH of the mobile phase, pH 5.8, wasobserved. The results are shown in FIG. 21 (results for Fv1-M71,Fv1-M73, Fv3-M71, and Fv3-M73 are shown in FIG. 21, while results forother clones are shown in FIGS. 17 and 19). Analyses were carried out inthe same manner as in Example 10 and the pH dependencies of thedissociation rate constants of all of the eleven types of clones areshown in Table 12.

TABLE 12 pH Dependencies of Dissociation Rate Constants ofpH-Dependently- Binding Clones from Membrane-Type IL-6 Receptor, SR344pH 7.4 pH 5.8 pH Dependency Sample kd (1/s) kd (1/s) kd (pH 5.8)/kd (pH7.4) WT 2.5E−04 2.5E−04 1.00 H3pI/L73 2.6E−04 6.7E−04 2.59 Fv1-M716.1E−04 6.9E−03 11.29 Fv1-M73 3.7E−04 3.2E−03 8.80 Fv2-IgG1 3.4E−042.4E−03 7.18 Fv3-M71 9.1E−04 9.7E−03 10.74 Fv3-M73 4.9E−04 5.3E−03 10.88Fv4-IgG1 4.7E−04 2.6E−03 5.56 Fv4-IgG2 1.0E−03 1.8E−02 16.99 Fv4-M585.4E−04 9.5E−03 17.64 Fv4-M73 5.1E−04 5.1E−03 10.06

The ten types of obtained pH-dependently-binding clones demonstratedpH-dependent binding ability to the membrane-type IL-6 receptor.Moreover, all of Fv1-M71, Fv1-M73, Fv2-IgG1, Fv3-M71, Fv3-M73, Fv4-IgG1,Fv4-IgG2, Fv4-M58, and Fv4-M73 were found to demonstrate improvedpH-dependent binding to the membrane-type IL-6 receptor, in comparisonwith H3pI/L73-IgG1, for which the time until the antibody disappearsfrom the plasma as well as the time where the soluble IL-6 receptor andmembrane-type IL-6 receptor are bound by the antibody in the body werefound to be prolonged considerably in comparison with WT, as shown incynomolgus monkeys in Example 9.

[Example 15] PK/PD Test of pH-Dependently-Binding Antibodies HavingOptimized Variable and Constant Regions Using Cynomolgus MonkeysConstruction of Known High-Affinity Anti-IL-6 Receptor Antibody

A mammalian cell expression vector was constructed to express thehigh-affinity anti-IL-6 receptor antibody VQ8F11-21 hIgG1 described inUS 2007/0280945 A1 (US 2007/0280945 A1, amino acid sequences 19 and 27),as a known high-affinity anti-IL-6 receptor antibody. An antibodyvariable region was constructed by PCR combining synthetic oligo-DNAs(assembly PCR). The constant region was amplified by PCR from theexpression vector used in Example 1. The antibody variable region andantibody constant region were ligated by assembly PCR and inserted intoa vector for expression in mammals. The resulting H chain and L chainDNA fragments were inserted into mammalian cell expression vectors toconstruct the H chain expression vector and L chain expression vector ofinterest. The nucleotide sequences of the resulting expression vectorswere determined by a method known among persons with ordinary skill inthe art. Expression and purification were carried out using theconstructed expression vectors. Expression and purification were carriedout using the method described in Example 1 to obtain the high-affinityanti-IL-6 receptor antibody (high affinity Ab).

PK/PD Test in Cynomolgus Monkeys

The pharmacokinetics and pharmacological efficacy were evaluated incynomolgus monkeys for the pH-dependently-binding antibodiesH3pI/L73-IgG1 and Fv1-M71, Fv1-M73, Fv2-IgG1, Fv3-M73, and Fv4-M73 andthe known high-affinity anti-IL-6 receptor antibody (high affinity Ab).H3pI/L73-IgG1, Fv1-M71, Fv1-M73, Fv2-IgG1, Fv3-M73, or Fv4-M73 wasadministered to cynomolgus monkeys by single-dose intravenousadministration at 0.5 mg/kg, while the high affinity Ab was administeredby single-dose intravenous administration at 1.0 mg/kg. Blood sampleswere collected before administration and over time. The plasmaconcentration of each antibody was measured in the same manner as inExample 9. The time courses of plasma concentrations of H3pI/L73-IgG1,Fv1-M71, Fv1-M73, Fv2-IgG1, Fv3-M73, and Fv4-M73, as well as the highaffinity Ab are shown in FIG. 21. In order to evaluate thepharmacological efficacy in terms of the degree to which the cynomolgusmonkey membrane-type IL-6 receptor is neutralized, cynomolgus monkeyIL-6 was administered subcutaneously into the lower backs of the animalsdaily at 5 μg/kg from day 3 to day 10 (from day 6 to day 10 with respectto the high affinity Ab) after the administration of antibody, in thesame manner as in Example 9. The CRP concentration of each animal wasmeasured 24 hours after each administration. The time courses of CRPconcentrations with the administration of each antibody are shown inFIG. 22. In order to evaluate the pharmacological efficacy in terms ofthe degree of neutralization of cynomolgus monkey soluble IL-6 receptor,the concentration of the unbound cynomolgus monkey soluble IL-6 receptorin cynomolgus monkey plasma was measured in the same manner as Example9. The time courses of the unbound cynomolgus monkey soluble IL-6receptor concentrations with the administration of each antibody areshown in FIG. 23.

As a result, the antibody concentrations in plasma were maintained highfor each of Fv1-M71, Fv1-M73, Fv2-IgG1, Fv3-M73 and Fv4-M73 incomparison with H3pI/L73-IgG1, while the concentrations of CRP and theunbound cynomolgus monkey soluble IL-6 receptor were maintained at lowlevels. Namely, this result showed that the time where the membrane-typeand soluble IL-6 receptors are bound by the antibody (or in other words,the duration of neutralization) was prolonged by the antibodies incomparison with H3pI/L73-IgG1.

In addition, these pH-dependently-binding anti-IL-6 receptor antibodieswere confirmed for their neutralization effects and sustained efficacyequal to or greater than that of the known high-affinity anti-IL-6receptor antibody (high affinity Ab) administered at 1.0 mg/kg, at onlyhalf the dosage thereof, i.e., at 0.5 mg/kg. Therefore, thepH-dependently-binding antibodies were elucidated to have theneutralization effects and sustained efficacy superior to those of theknown high-affinity anti-IL-6 receptor antibody.

Those antibodies shown in Table 12 for which PK/PD tests were notcarried out using cynomolgus monkeys as in this test, have also beenconfirmed to demonstrate improved pH-dependent binding to themembrane-type IL-6 receptor in comparison with H3pI/L73-IgG1. Therefore,the time during which the membrane-type and soluble IL-6 receptor arebound by the antibodies (or in other words, the duration ofneutralization and sustained neutralization effects) are also thought tobe prolonged for the antibodies in comparison with H3pI/L73-IgG1.

In Example 9, for H3pI/L73-IgG1, the time until the antibody disappearsfrom the plasma as well as the time where the soluble IL-6 receptor andmembrane-type IL-6 receptor are bound by the antibody in the body(sustained neutralization effects) were found to be prolongedconsiderably as compared with WT. Fv1-M71, Fv1-M73, Fv2-IgG1, Fv3-M71,Fv3-M73, Fv4-IgG1, Fv4-IgG2, Fv4-M58, and Fv4-M73, having superiorsustained neutralization effects to H3pI/L73-IgG1, are therefore thoughtto have remarkably improved sustained neutralization effects as comparedwith WT.

In contrast to anti-IL-6 receptor antibodies, the pH-dependent-bindinganti-IL-6 receptor antibodies that are made to strongly bind to theantigen at the pH in the plasma of pH 7.4 but only weakly bind to theantigen at the pH in endosomes of pH 5.8, make it possible to reduce thepatient dosage and administration frequency of the anti-IL-6 receptorantibody, and as a result, they can considerably reduce the totaladministration amount. Therefore, the pH-dependently-binding anti-IL-6receptor antibodies are thought to be extremely superior as apharmaceutical for use as an IL-6 antagonist.

[Example 16] Construction of pH-Dependently Binding Anti-IL-6 AntibodyExpression and Purification of Anti-IL-6 Antibody

In Examples 1 to 15, a plurality of humanized anti-IL-6 receptorantibodies that pH-dependently bind to the IL-6 receptor weresuccessfully created by imparting the dependency through introducinghistidine substitutions and the like into the variable region, inparticular, the CDR sequences of the humanized anti-IL-6 receptorantibodies. It was found that all of these antibodies repeatedly bind tothe IL-6 receptor and demonstrate a considerable improvement in PK/PD.

Therefore, it was confirmed that the pH-dependent ability of an antibodyto bind to an antigen could be confered to another antibody that bindsto an antigen other than the IL-6 receptor using a similar method. HumanIL-6 was selected as the antigen, and an anti-IL-6 antibody includingthe H chain (WT) (amino acid sequence: SEQ ID NO: 62) and L chain (WT)(amino acid sequence: SEQ ID NO: 63), which binds to IL-6 as describedin WO 2004/039826, (“Anti-IL6 wild type”) was constructed. Using amethod known to those skilled in the art, gene fragments encoding theantibody amino acid sequences of interest were inserted into mammaliancell expression vectors to construct the H chain expression vector and Lchain expression vector of interest. The nucleotide sequences of theresulting expression vectors were determined using a method known to askilled person. Anti-IL6 wild type was expressed and purified by themethod described in Example 1.

Construction of pH-Dependent Anti-IL-6 Antibody

To confer the pH-dependent ability of the antibody to bind to IL-6,histidine substitutions were introduced into the amino acids in CDR ofthe anti-IL-6 antibody (Anti-IL6 wild type) including the H chain (WT)(amino acid sequence: SEQ ID NO: 62) and L chain (WT) (amino acidsequence: SEQ ID NO: 63). By substituting histidine in the CDR aminoacids and subsequently screening, several clones that demonstrate thepH-dependent binding were obtained. The binding at pH 5.5 wassignificantly reduced as compared with the binding at pH 7.4. Thepositions of histidine substitution in the pH-dependent clones are shownin Table 13. The examples include “Anti-IL6 clone 1” including the Hchain (c1) (amino acid sequence: SEQ ID NO: 64) and L chain (c1) (aminoacid sequence: SEQ ID NO: 65), and “Anti-IL-6 clone 2” including the Hchain (c1) (amino acid sequence: SEQ ID NO: 64) and L chain (c2) (aminoacid sequence: SEQ ID NO: 66). Anti-IL6 clone 1 and Anti-IL-6 clone 2were expressed and purified by the method described in Example 1.

TABLE 13 Positions of Histidine Substitution in pH-dependent clones H32,H59, H61, H99 L53, L54, L90, L94Analysis of Binding of pH-Dependent Clones to Human IL-6

Kinetic analysis of antigen-antibody reactions at pH 5.5 and pH 7.4 wascarried out using a Biacore T100™ surface plasmon resonance system (GEHealthcare) for the three types of antibodies prepared as mentionedabove: Anti-IL6 wild type, Anti-IL6 clone 1, and Anti-IL-6 clone 2(buffer: DPBS(−) (pH 7.4 or pH 5.5), 150 mM NaCl). The antibodies werebound to a sensor chip on which recomb-protein A/G (Pierce) wasimmobilized by amine coupling, and then human IL-6 (Toray) adjusted toan appropriate concentration was injected on the chip as an analyte. Allthe measurements were carried out at 37° C. Association rate constantsk_(a) (1/Ms) and dissociation rate constants k_(d). (1/s) werecalculated using Biacore T100™ Evaluation Software (GE Healthcare), anddissociation constants KD (M) were calculated based on those values(Table 14). Furthermore, the ratio of affinity at pH 5.5 and pH 7.4 wascalculated for each clone to evaluate the pH-dependent binding.

TABLE 14 Comparison of Binding of pH-Dependent Clones to IL-6 KD (pH5.5)/ Sample pH ka (1/Ms) kd (1/s) KD (M) KD (pH 7.4) Wild type pH 7.42.05E+07 3.91E−04 1.91E−11 0.8 pH 5.5 1.52E+07 2.45E−04 1.61E−11 clone1pH 7.4 1.07E+07 4.71E−03 4.38E−10 10.3 pH 5.5 2.05E+06 9.26E−03 4.52E−09clone2 pH 7.4 8.96E+06 2.63E−03 2.94E−10 13.5 pH 5.5 2.76E+06 1.10E−023.98E−09

The ratio of affinity at pH 5.5 and pH 7.4 ((KD)(pH 5.5)/(KD)(pH 7.4))calculated, which indicates the pH-dependent binding to human IL-6, was0.8, 10.3, and 13.5 for Anti-IL6 wild type, Anti-IL6 clone 1, andAnti-IL6 clone 2, respectively. That is, the pH-dependent bindingability of each clone is more than 10 times greater than that of WT. Thesensorgrams of Anti-IL-6 clone 2 at pH 7.4 and pH 5.5 are shown in FIG.26.

Thus, it was shown that, as in the case of the anti-IL-6 receptorantibodies, pH-dependently binding anti-IL-6 antibodies that bind to theantigen strongly under plasma neutral conditions, but weakly underintraendosomal acidic conditions can be constructed by introducinghistidine substitutions and the like mainly into the CDR amino acidsequences. As indicated in Examples 1 to 15, an anti-IL-6 receptorantibody that has the pH-dependent binding ability repeatedly binds tothe IL-6 receptor and PK/PD is remarkably improved. That is, it wassuggested that Anti-IL-6 clone 1 and Anti-IL-6 clone 2, which have thepH-dependent binding ability, repeatedly bind to more antigens withsignificantly improved PK/PD, as compared with Anti-IL6 wild type.

[Example 17] Construction of pH-Dependently Binding Anti-IL-31 ReceptorAntibody Expression and Purification of Anti-IL-31 Receptor Antibody

In Examples 1 to 15, a plurality of humanized anti-IL-6 receptorantibodies that pH-dependently bind to the IL-6 receptor weresuccessfully created by conferring the pH dependency through introducinghistidine substitutions and the like into the variable region, inparticular, the CDR sequences of the humanized anti-IL-6 receptorantibodies. It was found that all of these antibodies repeatedly bind tothe IL-6 receptor and demonstrate a considerable improvement of PK/PD.

Therefore, it was confirmed that the pH dependent ability of an antibodyto bind to an antigen could be confered to another antibody that bindsto an antigen other than the IL-6 receptor using a similar method. MouseIL-31 receptor was selected as the antigen, and an anti-IL-31 receptorantibody including the H chain (WT) (amino acid sequence: SEQ ID NO: 67)and L chain (WT) (amino acid sequence: SEQ ID NO: 68), which binds tothe mouse IL-31 receptor as described in WO 2007/142325, (“Anti-IL31Rwild type”) was constructed. Using a method known to those skilled inthe art, gene fragments encoding the amino acid sequences of interestwere inserted into mammalian cell expression vectors to construct the Hchain expression vector and L chain expression vector of interest. Thenucleotide sequences of the resulting expression vectors were determinedusing a method known to a skilled person. Anti-IL31R wild type wasexpressed and purified by the method described in Example 1.

Construction of pH-Dependent Anti-IL-31 Receptor Antibody

To confer the pH-dependent ability of the antibody to bind to the IL-31receptor, histidine substitutions were introduced into the amino acidsof CDR of the anti-IL-31 receptor antibody (Anti-IL31R wild type)including the H chain (WT) (amino acid sequence: SEQ ID NO: 67) and Lchain (WT) (amino acid sequence: SEQ ID NO: 68). By histidinesubstitutions in the CDR amino acids and subsequent screening, severalclones that demonstrate the pH-dependent binding were obtained. Thebinding at pH 5.5 was significantly reduced as compared with the bindingat pH 7.4. The position of histidine substitution in the pH-dependentclones is shown in Table 15. An example is “Anti-IL31R clone 1”including the H chain (c1) (amino acid sequence: SEQ ID NO: 69) and Lchain (WT). Anti-IL31R clone 1 was expressed and purified using themethod described in Example 1.

TABLE 15 Position of Histidine Substitution in pH-dependent clones H33Analysis of Binding of pH-Dependent Clones to Soluble IL-31 Receptor

Kinetic analysis of antigen-antibody reactions at pH 5.5 and pH 7.4 wascarried out using a Biacore T100™ surface plasmon resonance system (GEHealthcare) for the two types of antibodies prepared as mentioned above:Anti-IL31R wild type and Anti-IL31R clone 1 (buffer: DPBS (−) (pH 7.4 orpH 5.5), 150 mM NaCl, 0.01% TWEEN® 20 (polyoxyethelene sorbitanmonolaurate), 0.02% NaN₃). The antibodies were bound to a sensor chip onwhich recomb-protein A/G (Pierce) was immobilized by amine coupling, andthen the soluble mouse IL-31 receptor (prepared according to the methoddescribed in WO 2007/142325) adjusted to an appropriate concentrationwas injected therein as an analyte. All the measurements were carriedout at 25° C. Association rate constants k_(a) (1/Ms) and dissociationrate constants k_(d). (1/s) were calculated using Biacore T100™Evaluation Software (GE Healthcare), and dissociation constants KD (M)were calculated based on those values (Table 16). Furthermore, the ratioof affinity at pH 5.5 and pH 7.4 was calculated for each clone toevaluate the pH-dependent binding.

TABLE 16 Comparison of Binding of pH-Dependent Clones to Mouse IL-31Receptor KD (pH 5.5)/ Sample pH ka (1/Ms) kd (1/s) KD (M) KD (pH 7.4)Wild type pH 7.4 1.40E+05 3.40E−03 2.30E−08 3.2 pH 5.5 5.10E+05 3.80E−037.40E−08 clone1 pH 7.4 1.70E+05 3.30E−03 2.20E−08 1000.0 pH 5.5 1.10E+032.40E−02 2.20E−05

The ratio of affinity at pH 5.5 and pH 7.4 ((KD)(pH 5.5)/(KD)(pH 7.4))calculated, which indicates the pH-dependent binding to the mouse IL-31receptor, was 3.2 and 1000 for Anti-IL31R wild type and Anti-IL31R clone1, respectively. That is, the pH-dependent binding ability of Anti-IL31Rclone 1 is about 300 times greater than that of WT. The sensorgrams forAnti-IL31R clone 1 at pH 7.4 and pH 5.5 are shown in FIG. 27.

Thus, it was shown that, as in the cases of the anti-IL-6 receptorantibodies and anti-IL-6 antibodies, pH-dependent binding anti-IL-31receptor antibodies that bind to the antigen strongly under plasmaneutral conditions, but weakly under intraendosomal acidic conditionscan be constructed by introducing histidine substitutions and the likemainly into the CDR amino acid sequences. As indicated in Examples 1 to15, an anti-IL-6 receptor antibody that has the pH-dependent bindingability repeatedly binds to the IL-6 receptor and PK/PD is remarkablyimproved. That is, it was suggested that Anti-IL31R clone 1, which hasthe pH-dependent binding ability, repeatedly binds to more antigens withsignificantly improved PK/PD, as compared with Anti-IL31R wild type.

[Example 18] Repetitive Binding to Antigen by pH-Dependently BindingAntibody Expression and Purification of Antibody Administered to Mice

The four types of humanized IL-6 receptor antibodies described belowwere prepared. As the antibodies that do not pH-dependently bind to theIL-6 receptor, WT-IgG1 including H (WT) (amino acid sequence: SEQ ID NO:9) and L (WT) (amino acid sequence: SEQ ID NO: 10), and H54/L28-IgG1including H54 (amino acid sequence: SEQ ID NO: 70) and L28 (amino acidsequence: SEQ ID NO: 12) were expressed and purified using the methodindicated in Example 1. As the antibodies that pH-dependently bind tothe IL-6 receptor, H170/L82-IgG1 of Example 3 including H170 (amino acidsequence: SEQ ID NO: 4) and L82 (amino acid sequence: SEQ ID NO: 7), andFv4-IgG1 of Example 10 including VH3-IgG1 (SEQ ID NO: 23) and VL3-CK(SEQ ID NO: 27), were expressed and purified using the method indicatedin Example 1.

Analysis of Binding of Each Type of Antibody to Soluble IL-6 Receptor

Kinetic analysis of antigen-antibody reactions at pH 7.4 and pH 5.8 wascarried out using a Biacore T100™ surface plasmon resonance system (GEHealthcare) for the four types of antibodies prepared: WT-IgG1,H54/L28-IgG1, H170/L82-IgG1, and Fv4-IgG1 (buffer: 10 mM IVIES (pH 7.4or pH 5.8), 150 mM NaCl, 0.05% Surfactant P20 (polyoxyethelene sorbitanmonolaurate)). The antibodies were bound to a sensor chip on whichrecomb-protein A/G (Pierce) was immobilized by amine coupling, and SR344adjusted to an appropriate concentration was injected therein as ananalyte. The association with and dissociation from SR344 of each typeof antibody were observed on a real-time basis. All the measurementswere carried out at 37° C. Association rate constants k_(a) (1/Ms) anddissociation rate constants k_(d). (1/s) were calculated using BiacoreT100™ Evaluation Software (GE Healthcare), and dissociation constants KD(M) were calculated based on those values (Table 17).

TABLE 17 Comparison of Association Rates (k_(a)), Dissociation Rates(k_(d)), and Dissociation Constants of Each Type of Antibody AgainstSoluble IL-6 Receptor (SR344) pH 7.4 pH 5.8 pH Dependency Sample ka(1/Ms) KD (1/s) KD (M) ka (1/Ms) KD (1/s) KD (M) KD (pH 5.8)/KD (pH 7.4)KD (pH 5.8)/KD (pH 7.4) WT-IgG1 4.9E+05 9.4E−04 1.9E−09 8.9E+05 2.7E−033.1E−09 2.9 1.6 H54/L28-IgG1 8.3E+05 1.4E−03 1.7E−09 2.4E+06 2.7E−031.1E−09 2.0 0.7 H170/L82-IgG1 6.7E+05 1.1E−03 1.6E−09 1.2E+05 1.3E−021.0E−07 11.4 61.9 Fv4-IgG1 9.8E+05 9.5E−04 9.7E−10 1.4E+06 3.7E−022.6E−08 38.8 27.3

The ratio of affinity (KD) at pH 5.8 and pH 7.4 for each antibody wascalculated. The KD ratio, which indicates the pH-dependent binding toSR344, was 1.6, 0.7, 61.9, and 27.3 for WT-IgG1, H54/L28-IgG1,H170/L82-IgG1, and Fv4-IgG1, respectively. In addition, the ratio ofdissociation rate (k_(d)) at pH 5.8 and pH 7.4 for each antibody wascalculated. The k_(d) ratio, which indicates the pH-dependentdissociation rate for SR344, was 2.9, 2.0, 11.4, and 38.8 for WT-IgG1,H54/L28-IgG1, H170/L82-IgG1, and Fv4-IgG1, respectively. Thus, it wasconfirmed that H170/L82-IgG1 and Fv4-IgG1 demonstrate the pH-dependentbinding, while the conventional antibodies WT-IgG1 and H54/L28-IgG1hardly exhibit the ability. In addition, since the affinity (KD) ofthese antibodies at pH 7.4 was nearly equal, their ability to bind toSR344 in the plasma was thought to be equivalent.

In Vivo Pharmacokinetics Test Using Mice

The pharmacokinetics of SR344 and the anti-human IL-6 receptor antibodywere evaluated following administration of SR344 (human IL-6 receptor,prepared in Example 1) only or simultaneous administration of SR344 andthe anti-human IL-6 receptor antibody to mice that do not express thehuman IL-6 receptor (C57BL/6J; the anti-human IL-6 receptor antibodiesdo not bind to the mouse IL-6 receptor). An SR344 solution (5 μg/mL) ora mixed solution containing SR344 and the anti-human IL-6 receptorantibody (5 μg/mL and 0.1 mg/mL, respectively) was administered into acaudal vein by single-dose administration at 10 mL/kg. Since theanti-human IL-6 receptor antibody was present in an adequate excessamount relative to SR344, it was thought that nearly all of the SR344molecules were bound by the antibody. Blood samples were collected at 15minutes, 2 hours, 8 hours, 1 day, 2 days, 3 days, 4 days, 7 days, 14days, 21 days, and 28 days after administration. The collected bloodsamples were immediately centrifuged for 15 minutes at 15,000 rpm and 4°C. to obtain the plasma. The plasma separated was stored in a freezerset to −20° C. or lower until the time of measurement. Above-describedWT-IgG1, H54/L28-IgG1, H170/L82-IgG1, and Fv4-IgG1 were used as theanti-human IL-6 receptor antibodies.

Measurement of Anti-Human IL-6 Receptor Antibody Plasma Concentration byELISA

The concentration of human IL-6 receptor antibody in mouse plasma wasmeasured by ELISA. Anti-human IgG (γ-chain specific) F(ab′)2 antibodyfragment (Sigma) was dispensed onto a Nunc-ImmunoPlate MaxiSorp (NalgeNunc International) and allowed to stand overnight at 4° C. to prepareanti-human IgG-immobilized plates. Calibration curve samples havingplasma concentrations of 0.8, 0.4, 0.2, 0.1, 0.05, 0.025, and 0.0125μg/mL, and mouse plasma samples diluted 100-fold or more were prepared.200 μL of 20 ng/mL SR344 was added to 100 μL of the calibration curvesamples and plasma samples, and then the samples were allowed to standfor 1 hour at room temperature. Subsequently, the samples were dispensedinto the anti-human IgG-immobilized plates, and allowed to stand for 1hour at room temperature. Then, Biotinylated Anti-Human IL-6R Antibody(R&D) was added to react for 1 hour at room temperature. Subsequently,Streptavidin-PolyHRP80 (Stereospecific Detection Technologies) was addedto react for 1 hour at room temperature, and chromogenic reaction wascarried out using TMP One Component HRP Microwell Substrate (BioFXLaboratories) as a substrate. After stopping the reaction with 1 Nsulfuric acid (Showa Chemical), the absorbance at 450 nm was measured bya microplate reader. The concentration in mouse plasma was calculatedfrom the absorbance of the calibration curve using the analyticalsoftware SOFTmax PRO (Molecular Devices). The time course of plasmaconcentration after intravenous administration as measured by thismethod is shown in FIG. 28.

Measurement of SR344 Plasma Concentration by Electrochemiluminescence

The concentration of SR344 in mouse plasma was measured byelectrochemiluminescence. SR344 calibration curve samples adjusted toconcentrations of 2000, 1000, 500, 250, 125, 62.5, and 31.25 pg/mL, andmouse plasma samples diluted 50-fold or more were prepared. The sampleswere mixed with a solution of Monoclonal Anti-human IL-6R Antibody (R&D)ruthenium-labeled with Sulfo-Tag NHS Ester (Meso Scale Discovery),Biotinylated Anti-human IL-6R Antibody (R&D), and WT-IgG1, and thenallowed to react overnight at 37° C. The final concentration of WT-IgG1was 333 μg/mL, which is in excess of the concentration of anti-humanIL-6 receptor antibody contained in the samples, for the purpose ofbinding nearly all of the SR344 molecules in the samples to WT-IgG1.Subsequently, the samples were dispensed into an MA400 PR StreptavidinPlate (Meso Scale Discovery), and allowed to react for 1 hour at roomtemperature, and washing was performed. Immediately after Read Buffer T(×4) (Meso Scale Discovery) was dispensed, the measurement was performedby the Sector PR 400 Reader (Meso Scale Discovery). The SR344concentration was calculated based on the response of the calibrationcurve using the analytical software SOFTmax PRO (Molecular Devices). Thetime course of SR344 plasma concentration after intravenousadministration as measured by this method is shown in FIG. 29.

Effects of pH-Dependent Binding

With respect to the time course of antibody concentration of WT-IgG1 andH54/L28-IgG1, which do not demonstrate the pH-dependent binding, andH170/L82-IgG1 and Fv4-IgG1, which demonstrate the pH-dependent binding,the time course of concentration was roughly identical for WT-IgG1,H54/L28-IgG1 and Fv4-IgG1, while H170/L82-IgG1 was eliminated slightlymore rapidly. The data of the time course of plasma concentration wasanalyzed by the pharmacokinetics analysis software WinNonlin(Pharsight). The half-lives in the plasma of WT-IgG1, H54/L28-IgG1,Fv4-IgG1, and H170/L28-IgG1 were 21.0, 28.8, 26.2, and 7.5 days,respectively.

As described in Example 2, when the antigen is a soluble antigen, anadministered antibody binds to the antigen in the plasma, and isretained in the plasma in the form of an antigen-antibody complex.Generally, in contrast to extremely long plasma retention time of anantibody (the elimination rate is extremely low) due to the function ofFcRn, the plasma retention time of an antigen is short (the eliminationrate is high). Thus, an antigen that is bound to an antibody has aprolonged plasma retention time similar to that of an antibody (theelimination rate is extremely low). Similarly, when the antigen ofhumanized IL-6 receptor antibody, SR344 (soluble human IL-6 receptor),was administered alone, SR344 was extremely rapidly eliminated (plasmahalf-life: 0.2 days). However, in the case of concurrent administrationof SR344 with a conventional antibody, WT-IgG1 or H54/L28-IgG1, whichdoes not demonstrate the pH-dependent binding, the elimination rate ofSR344 was considerably reduced, and the plasma retention time of SR344was prolonged (plasma half-life: 5.3 days for WT-IgG1, 6.3 days forH54/L28-IgG1). This is because nearly all of the SR344 molecules werebound by the antibodies administered together, and thus SR344 bound bythe antibodies had a prolonged plasma retention time similar to that ofthe antibody, due to the function of FcRn as described above.

In the case of concurrent administration of SR344 with the H170/L82-IgG1or Fv4-IgG1 antibody, which demonstrates the pH-dependent binding, theelimination of SR344 was significantly rapid (plasma half-life: 1.3 daysfor H170/L82-IgG1, 0.6 days for Fv4-IgG1), as compared to the case ofconcurrent administration with WT-IgG1 or H54/L28-IgG1. This tendencywas particularly prominent for Fv4-IgG1. Since the affinity of Fv4-IgG1at pH 7.4 is equivalent to or stronger than that of WT-IgG1 andH54/L28-IgG1, it is thought that nearly all of the SR344 molecules werebound to Fv4-IgG1. Even though Fv4-IgG1 demonstrates equivalent orslightly longer plasma retention and slower elimination compared toWT-IgG1 and H54/L28-IgG1, the elimination of SR344 bound to Fv4-IgG1 wasextremely rapid. This can be explained by the concept of the presenttechnology shown in FIG. 4. In the case of conventional antibodies thatdo not demonstrate the pH-dependent binding, an antibody-soluble antigencomplex is taken up into endosomes by pinocytosis in the plasma, andbinds to FcRn expressed in endosomes under intraendosomal acidicconditions. Since the antibody-soluble antigen complex bound to FcRntransfers to the cell surface as it is, and again returns to the plasma,the antigen bound to the antibody has a prolonged plasma retention timesimilar to that of the antibody (the elimination is extremely slow). Onthe other hand, in the case of antibodies that demonstrate thepH-dependent binding, the antigen dissociates from the antibody underintraendosomal acidic conditions, and thus only the antibody binds toFcRn and returns again to the plasma. Since the antigen dissociated fromthe antibody is degraded in lysosomes without returning to the plasma,the elimination of antigen is extremely rapid as compared to the case ofantibodies that do not demonstrate the pH-dependent binding. Namely, inthe case of concurrent administration of SR344 with the WT-IgG1 orH54/L28-IgG1 antibody, which does not demonstrate the pH-dependentbinding, the elimination of SR344 is slow to the similar degree as theantibody, since SR344 binds to WT-IgG1 or H54/L28-IgG1 both in plasmaand endosomes. In contrast, in the case of concurrent administration ofSR344 with the H170/L82-IgG1 or Fv4-IgG1 antibody, which demonstratesthe pH-dependent binding, the elimination of SR344 is extremely rapid,since SR344 dissociates from the antibody in the intraendosomal low-pHenvironment. That is, since the H170/L28-IgG1 and Fv4-IgG1 antibodies,which demonstrate the pH-dependent binding, dissociate from SR344 in theintraendosomal low-pH environment, the majority of H170/L82-IgG1 orFv4-IgG1 that has returned again to the plasma with FcRn is thought tobe not bound to SR344. Thus, as shown in FIG. 4, it was revealed that,by dissociating from an antigen in the intraendosomal low-pH environmentand returning to the plasma with FcRn without binding to the antigen, anantibody that demonstrates the pH-dependent binding can again bind to anantigen in the plasma. It was also shown that, by repeating thisprocess, the antibody that demonstrates the pH-dependent binding canrepeatedly bind to multiple antigens. This is consistent with theBiacore™ surface plasmon resonance data shown in Example 7,demonstrating that pH-dependent antibodies can repeatedly bind toantigens. Thus, by enhancing the pH-dependent binding of an antibody toan antigen, the number of times of repetitive antigen binding can beincreased.

When the antigen is a soluble antigen, and the antigen binds to anantibody under plasma neutral conditions, but dissociates from theantibody in endosomes and the antibody returns to the plasma with FcRn,the antibody can again bind to an antigen under plasma neutralconditions. Thus, an antibody that has the ability to dissociate from anantigen under intraendosomal acidic conditions can bind to antigensmultiple times. As compared to when an antigen bound to an antibody doesnot dissociate from the antibody in endosomes (i.e., the antigen boundto the antibody returns to the plasma), if an antigen bound to anantibody dissociates from the antibody in endosomes, the plasmaelimination rate of the antigen is increased, since the antigen istransported to lysosomes and degraded. Thus, the plasma elimination rateof an antigen can be used as an index to determine whether an antibodycan bind to the antigen multiple times. Determination of the plasmaelimination rate of an antigen can be performed, for example, byadministering an antigen and an antibody in vivo, and then measuring theplasma antigen concentration after the administration, as shown in theExamples.

An antibody that demonstrates the pH-dependent binding can repeatedlybind to multiple antigens in contrast to the case of a conventionalantibody that does not demonstrate the pH-dependent binding. Thus, theamount of antibody administered can be considerably reduced, and theadministration intervals can be greatly prolonged.

The repetitive binding to multiple antigens of this mechanism is basedon pH-dependent antigen-antibody reaction. Thus, regardless of the typeof antigen, if an antibody demonstrating the pH-dependent binding thatbinds to an antigen at pH 7.4 of plasma but dissociates from the antigenat intraendosomal acidic pH can be constructed, then such an antibodycan repeatedly bind to multiple antigens. Accordingly, the presenttechnology is useful in that it can be applied not only to antibodies tothe IL-6 receptor, IL-6, and the IL-31 receptor, but generally to anyantibody to any antigen, regardless of the type of antigen.

1.-50. (canceled)
 51. A method of removing an antigen from plasma, themethod comprising: (a) identifying an individual in need of having anantigen removed from the individual's plasma; and (b) administering anantibody to the individual wherein the antibody binds to the antigenthrough the antigen-binding domain of the antibody and has aKD(pH5.8)/KD(pH7.4) value, defined as the ratio of KD for the antigen atpH 5.8 and KD for the antigen at pH 7.4, of 2 to 10,000, and wherein theantibody binds to the antigen in plasma in vivo and dissociates from thebound antigen under conditions present in an endosome in vivo, andwherein the antibody is a human IgG or a humanized IgG.
 52. The methodof claim 51, wherein the antigen is a soluble antigen.
 53. The method ofclaim 51, wherein the antibody is a humanized IgG.
 54. The method ofclaim 51, wherein KD is determined using a surface plasmon resonancetechnique in which the antibody is immobilized, the antigen serves asanalyte, and the following conditions are used: 1.0 mM MES buffer, 0.05%polyoxyethylene sorbitan monolaurate, and 150 mM NaCl at 37° C.
 55. Themethod of claim 51, wherein the KD(pH5.8)/KD(pH7.4) value is 2 to 1,000.56. The method of claim 51, wherein the KD(pH5.8)/KD(pH7.4) value is 40to 1,000.
 57. The method of claim 51, wherein the KD(pH5.8)/KD(pH7.4)value is 2 to
 400. 58. The method of claim 51, wherein theKD(pH5.8)/KD(pH7.4) value is 10 to
 400. 59. The method of claim 51,wherein the KD(pH5.8)/KD(pH7.4) value is 30 to
 400. 60. The method ofclaim 51, wherein the KD(pH5.8)/KD(pH7.4) value is 40 to
 400. 61. Amethod of removing an antigen from plasma, the method comprising: (a)identifying an individual in need of having an antigen removed from theindividual's plasma; (b) administering an antibody to the individualwherein the antibody binds to the antigen through the antigen-bindingdomain of the antibody and has a KD(pH5.8)/KD(pH7.4) value, defined asthe ratio of KD for the antigen at pH 5.8 and KB for the antigen at pH7.4, of 2 to 1,000, and wherein the antibody binds to the antigen inplasma in vivo and dissociates from the bound antigen under conditionspresent in an endosome in vivo, and wherein the antibody is a human IgGor a humanized IgG.
 62. The method of claim 61, wherein the antigen is asoluble antigen.
 63. The method of claim 61, wherein theKD(pH5.8)/KD(pH7.4) value is 10 to
 400. 64. The method of claim 61,wherein the KD(pH5.8)/KD(pH7.4) value is 30 to
 400. 65. The method ofclaim 61, wherein the KD(pH5.8)/KD(pH7.4) value is 40 to
 400. 66. Amethod of removing an antigen from plasma, the method comprising: (a)identifying an individual in need of having an antigen removed from theindividual's plasma; (b) administering an antibody to the individualwherein the antibody binds to the antigen through the antigen-bindingdomain of the antibody and has a KD(pH5.8)/KD(pH7.4) value, defined asthe ratio of KD for the antigen at pH 5.8 and KD for the antigen at pH7.4, of 2 to 400, and wherein the antibody binds to the antigen inplasma in vivo and dissociates from the bound antigen under conditionspresent in an endosome in vivo, and wherein the antibody is a human IgGor a humanized IgG.
 67. The method of claim 66, wherein the antigen is asoluble antigen.
 68. The method of claim 66, wherein theKD(pH5.8)/KD(pH7.4) value is 10 to
 400. 69. The method of claim 66,wherein the KD(pH5.8)/KD(pH7.4) value is 30 to
 400. 70. The method ofclaim 66, wherein the KD(pH5.8)/KD(pH7.4) value is 40 to 400.